THE REGIONAL GEOLOGY OF THE DAVENPORT AND …Tungsten ores are mined on the Hatches Creek, Mosquito Creek, and Wauchope min-ing fields. The total white population is about one hundred

COMMONWEALTH O F AUSTRALI A

DEPARTMENT O F NATIONA L D E V E L O P M E N T

BUREAU O F MINERA L RESOURCES , GEOLOG Y AN D GEOPHYSIC S

007930 Report No. 58

THE REGIONA L GEOLOG Y O F TH E DAVENPORT AN D MURCHISO N RANGES ,

NORTHERN TERRITOR Y

BY;

K. G . SMTH , J . R . STEWART , AN D J . W . SMIT H

Issued unde r th e Authorit y c f Senato r the Hon . W . H . Spooner , Minister fo r Nationa l Developmen t

1961

C O M M O N W E A L T H O F A U S T R A L I A

DEPARTMENT O F NATIONA L DEVELOPMEN T

BUREAU O F MINERA L RESOURCES , GEOLOG Y AN D GEOPHYSIC S

Report No. 58

THE REGIONA L GEOLOG Y O F TH E DAVENPORT AN D MURCHISO N RANGES ,

NORTHERN TERRITOR Y

B Y

K. G . SMITH , J . R . STEWART , AN D J . W . SMIT H

Issued unde r th e Authorit y o f Senato r the Hon . W . H . Spooner , Minister fo r Nationa l Developmen t

1961 l Q

r

COMMONWEALTH O F AUSTRALIA

D E P A R T M E N T O F N A T I O N A L D E V E L O P M E N T

Minister: SENATO R THE HON. W . H. SPOONER , M.M.

Secretary: H . G. RAGGATT, C.B.E .

B U R E A U O F M I N E R AL RESOURCES , G E O L O G Y A N D G E O P H Y S I C S

Director: J . M. RAYNER

This Rej%>rt was prepared in the Geological Branch zChief Geologist: N. H. FISHER

CONTENTS

Pa%e

SUMMARY .. . . . . . . . . . . . . . 1

INTRODUCTION .. . . . . . . . . . . 3

Location . . . . . . . . . . . . . . . 3

Development . . . . . . . . . . . . 3 Access .. . . . . . . . . . . . . . 3 Communications . . . . . . . . . . . . 5 Climate .. . . . . . . . . . . . . . 5 Vegetation .. . . . . . . . . . . 5 Topography .. . . . . . . . . . . 6

GEOLOGICAL INVESTIGATION S . . . . . . . . . 6

Previous Investigation s . . . . . . . . . 6 Investigations i n adjoinin g areas . . . . . . . . . 7

1956 Surve y . . . . . . . . . . . . 7

GEOLOGY .. . . . . . . . . . . . . . 8

Nomenclature . . . . . . . . . . . . 8

Lower Proterozoi c . . . . . . . . . . . . 8 ? Upper Proterozoic . . . . . . . . . . . . 1 4 Cambrian . . . . . . . . . . . . 1 5 ? Tertiar y . . . . . . . . . . . . 1 7

ECONOMIC GEOLOG Y . . . . . . . . . . . . 1 7

Tungsten . . . . . . . . . . . . . . . 1 7

Uranium . . . . . . . . . . . . . . . 1 8

REFERENCES . . . . . . . . . . . . 2 0

APPENDIX : Petrographie description s b y K.R. Walker . . . 2 2

ILLUSTRATIONS

Fig. 1 Localit y Map . . . . . . . . . 3

Fig. 2 " " . . . . . . 4 Fig. 3 Tectoni c Ma p .. . . . . . . . 1 2

PLATE 1 . Regiona l Geologica l Map at back of Report.

SUMMARY

The are a o f tn e Davenpor t an d Murchiso n Ranges , whic h i s th e subjec t of this Report, i s covere d b y par t o f eac h o f the Barrow Creek, Bonney Well, Elkedra , and Frew River 1:250,000 Sheets . Th e ranges consis t mainl y of Lower Proterozoic arenite s o f the Hatche s Creek Group, whic h hav e bee n intrude d b y basi c igneou s rock s and by granite. I n the north-easter n part o f th e are a th e Hatche s Cree k Grou p rest s unconformabl y on older Lowe r Proterozoic sediments o f th e Warramung a Group . Th e age s o f severa l masse s o f granite , determined by radioactivity methods , rang e between 132 0 and 1440 million years. Fossiliferou s Middl e Cambria n sediments an d ? Tertiary sediments res t unconformabl y on the Warramunga Group, o n the Hatche s Creek Group , an d on igneous rocks .

The tungste n deposit s o f Hatche s Creek , which ar e th e mai n deposits o f economi c value i n the area , ar e describe d in another publication (Ryan , 1961) .

INTRODUCTION

Location: Th e Davenpor t an d Murchiso n Range s for m roughl y a diagonal t o the rectangle bounde d by the 134th and 136th meridians of east longitud e an d the 20t h and 22nd parallels of sout h latitude . Th e souther n extremit y o f the Davenpor t Range is almos t equidistant fro m the townships o f Alic e Spring s an d Tennant Creek; th e norther n extremit y o f the Murchiso n Range i s about twenty-five mile s sout h o f Tennan t Creek township.

Development: Th e are a i s divide d int o severa l larg e Pastora l Lease s an d Grazing Licences, an d tw o Nativ e Reservations . Th e Pastoral Lease s an d Grazing Licences ar e used fo r the raisin g o f cattle fo r beef . On e Native Reservatio n i s uninhabited ; th e other, named Warrabri, is bein g developed .

Tungsten ores ar e mined on the Hatche s Creek , Mosquito Creek, and Wauchope min-ing fields .

The tota l whit e populatio n i s abou t on e hundre d and fifty. Thi s figure fluctuate s i n accordance wit h the grad e o f tungsten ore s an d their marke t price .

Access: Th e bitumen-surface d Stuar t Highway , whic h link s Darwi n and Alice Springs provide s th e mai n acces s t o th e area . Th e highway crosse s th e western portio n o f the Davenport Rang e nea r th e smal l settlemen t o f Wauchope , which i s seventy-tw o mile s sout h of Tennant Cree k township . Fro m a poin t forty-tw o mile s sout h o f Wauchope a formed, earth-surfaced roa d lead s fro m th e Stuar t Highway , throug h Murray Down s Station an d Hatches Creek mining field , t o Kurinell i out-statio n an d Kurundi . A n extension o f this roa d serves Epenarr a Station. Fro m Kurund i th e roa d lead s bac k t o the Stuar t Highwa y at Bonney Well, which i s

3

T E N N A N T CREE K

BONNEY WEL L

ALROY — 1 » -

FREW RIVE R

, • ' H. T .Borrow Cret k

< , SP '

m BARRO W CREE K

W o u c h o p ^ T i ^

icy Semi-desert * ' / ^ \ , M u .

c r f y —

To Ammafoo and Alice Springs

ELKEDRA /3«*30'

L O C A L I T Y M A P , W I T H R E F E R E N C E T O A U S T R A L I A N 4 M I L E S E R I E S

SCALE

»

Reference

• Homestead Road

H Hotel V We//, with wmdpump

T Telephone Mine

P Police Station HOO' Spot Height

z Transceiver Boundary of Area

© s mapped i$S6. © Aerodrome

mapped i$S6.

Bureau of M intra/ Resources, Geology & 6eophysies. Oct I960.

4

eighteen mile s nort h o f Wauchope . A t a point two miles nort h of Kurundi Station a track leads t o the Mosquit o Cree k tungste n an d uraniu m workings an d thence t o the Stuar t Highway at McLaren Well. Eigh t mile s eas t o f Murray Downs Station a formed, earth-surfaced roa d leads t o Elkedra Station; fro m her e a roa d o f simila r typ e leads sout h to Ammaroo Statio n an d ultimately t o the Stuart Highwa y a t a point fifty-nin e mile s nort h of Alice Springs . Fro m each station , track s lea d to waterin g place s an d musterin g yard s fo r cattle . T o the eas t o f Hatches Cree k mining fiel d there ar e neithe r road s no r track s i n th e Davenpor t Range. Earth-surface d roads lead from Urandangi i n Queensland , vi a severa l statio n homesteads , t o Ammaroo an d Elkedra Stations. Al l the earth-surface d road s ma y become impassable fo r severa l day s afte r heav y rain .

The neares t railhea d is at Alice Springs. From its bas e a t Port Augusta the Common -wealth Railway s provid e tw o passenge r train s a wee k between Ma y and October, and one a week for th e remainde r of the year .

Landing ground s suitabl e fo r light aircraf t have been constructe d a t Elkedra, Epen-arra, Kurund i an d Murra y Down s Stations , a t Hatches Cree k settlement, an d at Warrabri. Alic e Springs an d Tennant Creek Airfields ar e suitabl e fo r heavy aircraft .

Communications: Norma l mail an d telephone service s are availabl e a t Wauchope on the Darwin-Alic e Spring s telegrap h line , bu t there ar e no scheduled surfac e mai l service s to the remainder o f the area .

From it s bas e a t Alic e Springs , Connella n Airways operates a regular mail , pass-enger, an d freigh t service , on e northboun d an d on e southboun d per week, t o Elkedra, Epenarra, Kurundi, an d Murra y Down s Station s an d the Hatche s Cree k settlement. Bot h Tennant Creek and Alice Spring s ar e port s o f cal l o n regular ai r service s between Adelaide and Darwin. Th e same airline operate s a regular servic e betwee n Brisban e an d Tennant Creek.

Elkedra, Epenarra , Kurundi, and Murray Downs Stations, Hatche s Cree k settlement , and Warrabr i Nativ e Reservatio n ar e linke d b y radi o telephon e wit h the Alic e Springs Base Station o f th e Roya l Flyin g Docto r Service . Thi s servic e provide s prompt medical attentio n and transmits an d receives telegrams .

Heavy good s ar e carrie d b y transpor t truck s o f th e semi-traile r type . Fleet s o f these vehicle s pl y betwee n Alic e Spring s an d th e norther n railhead o f Birdum, which i s som e three hundre d miles sout h of Darwin. Ore from the Hatche s Creek , Mosquito Creek, and Wauchope mining fields i s carrie d by road transport to the railhea d at Alice Springs.

Climate: Lon g ho t summer s an d short mild winters ar e usual. I n summer, shade temperatures frequentl y excee d on e hundre d an d te n degree s Fahrenheit : a t this period o f the year som e o f the miner s ceas e wor k for severa l months . Fiel d work is unpleasan t under summer conditions an d i s bes t performe d betwee n Ma y and September . Th e annual rainfal l i s normall y about twelv e inches ; th e heavies t fall s normall y occur between Novembe r and March. However , both rainfal l an d distribution ar e ver y unreliable. I n 1956 there were heav y falls o f rai n in every month from April t o October. Th e prevailing wind blows strongl y from the south-east .

Vegetation: I n area s o f outcrop , spinifex, mulga , and gidyea ar e common ; gidye a grows mos t commonl y i n area s wher e aci d volcanic rock s an d porphyries cro p out , but spinifex , which i s absen t fro m thes e areas , i s abundan t i n all othe r places. Ther e are many varieties of flowering shrubs . Eucalypt s lin e th e course s o f th e larger streams . I n semi-desert countr y

5

on the eastern an d western flank s o f the ranges there ar e man y varieties o f acacia . I n the easter n parts o f th e range s th e gastrolobiu m bus h i s common ; i t contain s a poison which i s fata l t o cattle.

Topography: Th e Davenpor t an d Murchison Ranges consist mainl y of long, almos t parallel, steepside d flat-toppe d ridges , separate d b y wid e fla t valleys . Th e tops o f the ridge s are abou t 165 0 fee t abov e se a level , an d 200-350 fee t abov e the floors o f the valleys . Th e ridges are strik e ridges ; ther e ar e fe w gap s i n them and therefore vehicl e access , acros s th e strike , is ver y difficult . Acces s alon g th e strik e i s comparativel y easy because vehicle s ca n generall y negotiate th e floor s o f th e valleys . Th e ranges ar e bounded to the eas t an d west by plains abou t 900 fee t abov e se a level , o n which low parallel sand-ridge s tren d north-west .

Several larg e stream s drai n from the range s t o the plains, where they disperse an d disappear; n o strea m whos e sourc e i s i n the range s reache s a river syste m which flows eithe r to the se a o r to an inland lake.

GEOLOGICAL INVESTIGATION S

Previous Investigation s too k plac e i n tw o phases . Th e period between 189 5 and 1914 wa s on e o f exploratio n an d prospecting , leadin g up to the firs t commercia l mining in 1914. In th e secon d period, between 191 4 and 1956, investigations wer e confine d to the mining fields an d small area s adjacen t to them.

In 1895 , H.Y.L . Brow n (Brown , 1895 ) mad e th e firs t geologica l investigations ; h e examined som e o f th e easter n par t o f th e Davenpor t Range and commented upon probable auri-ferous countr y withi n th e confine s o f th e present-da y Hatche s Cree k Wolfram Field . I n 1896 he mad e anothe r journe y throug h som e of the sam e country; h e travelled from Barrow Creek to Hatches Cree k an d th e abandone d Fre w Rive r Station , then returned alon g Hatches Cree k and proceeded sout h to Elkedra (Brown, 1897) .

A«A. Davidso n i n 1898-9 9 (Davidson , 1905 ) le d a prospectin g expeditio n which was financed b y th e Centra l Australia n Exploratio n Syndicate . Becaus e o f the undeveloped nature of th e countr y a t tha t time , th e Centra l Australia n Exploration Syndicate was intereste d onl y in the discover y o f a large , ric h orebody , peferabl y o f gold . Davidson' s party prospected most of the Davenpor t an d Murchiso n Ranges , bu t a lon g an d conscientious search , conducte d under conditions o f considerabl e hardship , faile d t o discove r an y orebodie s o f the typ e which would interest th e Syndicate . Nearl y al l th e smal l occurrence s o f copper , gold, and lead now known in th e are a wer e discovere d b y Davidson and his party , and D. Pedlar, a prospector in the party, found specimen s o f wolfra m i n th e Hatche s Cree k area , but the minera l was no t identified .

In 1902 , H.Y.L . Brow n (Brown , 1903 ) agai n visite d th e Davenport and Murchison Ranges an d fro m hi s geologica l observation s conclude d that there wer e larg e area s worth pros-pecting fo r gold. Thes e area s were mainly on the northern and north-eastern flank s o f the ranges , where th e sediment s wer e ver y different fro m those i n the range s themselves .

W.R. Murray , i n 190 6 (Murray , 1907) , le d a prospectin g party sponsored by the Department o f Mine s i n South Australia and directed hi s effort s toward s the discover y o f payable alluvial gold , but was unsuccessful .

6

In 191 4 Pedlar' s specimen s wer e identifie d a s wolfram; h e obtained a Government grant o f £5 0 an d returne d t o th e Hatche s Cree k area, where h e soo n pegged severa l leases . Within a shor t tim e severa l miner s wer e workin g o n the ne w field, whic h was inspecte d b y T.G. Olive r (1916) .

In 1940 , officer s o f th e Aerial , Geologica l an d Geophysica l Surve y of Northern Australia (A.G.G.S.N.A. ) geologicall y mappe d th e mine s a t Hatche s Cree k and at Wauchope and the area s immediatel y surroundin g them , a tota l o f abou t 80 square miles . Th e same organis -ation carrie d ou t aeria l photograph y ove r smal l area s nea r the Hatche s Cree k and Wauchope Wolfram Field s (A.G.G.S.N.A. , 1941) .

In 194 9 C.J . Sulliva n re-examine d th e wolfra m mine s a t Hatches Cree k (Sullivan , 1951) an d those o f the Wauchope Wolfram Fiel d (Sullivan , 1952) .

Tungsten ore s wer e discovere d a t Mosquit o Cree k i n 195 1 and secondary uranium ores i n 1955 ; thes e occurrence s were inspected by geologists o f the Burea u of Minera l Resources, Geology an d Geophysics (Jokli k & Tomich, 1951; Bell , 1953 ; Lord , 1955) .

P.S. Hossfel d (leade r o f th e Norther n Territory field partie s o f A.G.G.S.N.A . 1940-41) publishe d th e result s o f hi s geologica l observation s i n the Norther n Territory in 1954 ; h e made man y reference s t o th e geolog y o f the Davenpor t Range, and to that o f the Hatches Creek area i n particular .

Investigations i n adjoining areas nort h of the Murchiso n Range in the Tennan t Creek Goldfield hav e som e bearing o n the stratigraph y o f the Davenport Range - Murchiso n Range area . Owen (1942 , unpubl. ) mappe d a n are a o f abou t 45 0 square mile s o n the goldfield ; i n 1948-5 0 a fiel d part y fro m th e Geologica l Branc h o f th e Bureau of Minera l Resources, Geolog y and Geophysics mappe d th e regiona l geolog y o f abou t 2500 squar e miles (Ivanac , 1954) . Th e souther n limit o f thi s regiona l mappin g wa s a t abou t latitud e 1 9 45'S , which i s abou t 15* north of the northern limit o f the are a mappe d during the 195 6 survey o f the Davenpor t and Murchison Ranges.

1956 Survey : A fiel d part y fro m th e Geologica l Branch of the Bureau of Mineral Resources, Geolog y and Geophysics mappe d the whole o f the Davenport and Murchison Ranges a t a scale o f fou r mile s t o one inch i n 1956. Th e objects o f the surve y were t o map the geolog y o f the area a s a whol e an d to prospect for metals , includin g uranium. Th e field wor k was don e by K.G . Smith, J.R . Stewart , J.W . Smith, an d G.R. Ryan. G.R . Ryan confined his work to the mappin g of the geolog y o f th e Hatche s Cree k Wolfra m Fiel d an d to the detaile d mappin g of the surfac e and undergroun d working s o f th e mines ; thi s wor k is th e subjec t o f a separate bulleti n (Ryan , 1961). Th e other geologist s wer e responsibl e fo r the regiona l mappin g of the whole area .

Concurrently with the regiona l survey , the Geophysical Branch of the Bureau carrie d out airborn e scintillograp h an d airborn e magnetomete r survey s o f part s o f the Davenport and Murchison Ranges , i n whic h on e D.C. 3 an d tw o Auste r aircraft wer e used . On e Auster aircraf t made clos e examination s o f radioactiv e anomalie s detecte d fro m th e D.C . 3 aircraft; th e othe r surveyed thre e smal l areas selected by the geological field party (Livingstone , 1957) ; subsequently , radioactive anomalie s detecte d fro m this aircraf t wer e examine d on the groun d by officers o f the Geophysical Branch using car-born e scintillograp h equipmen t (Langron , 1957).

The geologica l surve y wa s mad e betwee n Apri l an d Octobe r 1956, and a total o f eighteen man-months was spen t i n the field . A n area of abou t eight thousand squar e miles , cover -ing part s o f th e Barro w Creek , Bonney Well, Elkedra , and Frew River Sheets , wa s mapped . Ai r

photographs taken by the Roya l Australian Air Forc e provided a complete photographi c cove r o f the area o n a scale o f 1:50,000 . Som e large-scale photographs , taken by A.G.G.S.N.A., wer e availabl e for th e are a o f the Hatche s Cree k Wolfram Field . Fiel d data were plotte d o n air photographs and then transferre d t o semi-controlle d mosaic s o f Barrow Creek, Bonney Well, an d Elkedra Sheets . Full ma p control was availabl e for the Frew River Sheet, an d the geolog y o f that are a was compile d on a slotte d templat e assembl y a t photo scale , whic h was then reduce d photographically to four-mile scale . Th e map on Plate 1 was produce d by fitting togethe r th e three semi-controlle d sheet s and th e controlle d shee t o f Fre w River.

GEOLOGY

Nomenclature

In this repor t th e standar d practice o f the Bureau of Minera l Resources wit h respec t to tim e division s o f the Precambria n is followed : tha t is , tw o main time divisions , Archaea n and Proterozoic, wit h the latte r divide d int o Lowe r Proterozoic an d Upper Proterozoic .

This practic e i s no t unifor m i n Australia , althoug h these division s withi n th e Pre -cambrian ar e universall y recognised . Som e State s follo w it ; other s adop t the practice o f South Australia an d Wester n Australia , plac e th e two older division s withi n th e Archaean , and restric t Proterozoic t o th e younges t division . Browne , edito r o f David (1950) , use d Lower , Middle, and Upper Precambrian . Hossfel d (1954 ) use d Archaeozoic an d Proterozoic an d divided the Protero -zoic int o Lower , Middle , an d Upper.

LOWER PROTEROZOI C

The oldes t rock s expose d ar e thos e o f th e Warramung a Group. Thi s Grou p was named formall y b y Ivanac (1954 ) i n the Tennan t Creek area; Owe n (1942) ha d previously use d th e term "Warramung a Series " fo r th e Precambria n sedimentar y rock s o f the Tennan t Creek area.

The Warramung a Grou p crop s ou t on the north-eastern an d north-western flank s o f the Davenpor t an d Murchiso n Ranges . Thes e rock s wer e mappe d in reconnaissance detai l only , the objec t bein g t o establis h th e structura l an d stratigraphic relationship s betwee n the m an d the sedimentary sequenc e whic h crop s ou t i n th e Ranges . The y crop out in isolated pinnacle s an d mesas whos e elevatio n i s rarel y mor e tha n 10 0 fee t abov e the leve l o f the surroundin g plain . The sedimentar y roc k types ar e sandstone , greywacke , sil t stone, shale , an d red and black banded chert. Som e rhyolites appea r to be conformable with the sediments .

The Warramung a Grou p ha s bee n strongl y folde d an d faulted an d has been intruded by basi c rocks , b y aci d porphyry , an d b y a microcline granit e whic h i s porphyriti c i n feldspar . Almost throughout , metamorphis m i s restricte d t o low-grad e therma l metamorphis m a t and near th e contac t wit h bot h granit e an d porphyry , evidence d b y narrow zones o f silicification . A fe w mica schist s were observed .

In th e are a mapped , th e discontinuit y o f outcrog prevented an y determination o f the regional structur e o f th e Group . Strike s rang e fro m 27 0 t o 04 0 , mostly in a general west -north-west direction . Thicknes s coul d be neither measure d nor estimated, becaus e o f the stron g folding an d poor outcrop.

The fiel d relationship s o f the Warramunga Group are: -

8

(a) I n the Tennan t Creek area (afte r Ivanac , 1954) :

(1) th e Warramunga Group has bee n intrude d by granite; (2) bot h th e Warramung a Grou p an d th e granit e whic h intrude s i t

are overlai n unconformabl y b y th e Hele n Spring s Volcanics , which ar e considere d t o be of Lower Cambrian age;

(3) th e fossiliferou s Gu m Ridge Formation , of lower Middl e Cambrian age, lie s unconformabl y o n th e Warramung a Group, on granite , and on the Hele n Springs Volcanics .

(b) I n the Davenpor t - Murchiso n Range area:

(1) th e Warramung a Group is overlai n unconformably by the unfossil -iferous sedimentar y sequenc e whic h constitute s mos t o f th e Davenport and Murchison Ranges;

(2) outcrop s o f bot h th e Warramung a Group and the sediment s o f the Davenport an d Murchiso n Ranges hav e been intrude d by granite ; but the granit e bodie s ma y not be al l o f the sam e age ;

(3) th e Warramung a Group , th e sediment s o f th e Davenpor t an d Murchison Ranges , an d som e o f th e granite s ar e conformabl y overlain b y fossiliferou s sediment s o f lowe r Middl e Cambrian age.

The fiel d evidenc e thu s establishe s a Precambrian age fo r the Warramunga Group . Earlier workers , e.g . Sulliva n (1951) , Noake s & Traves (1954) , an d Hossfeld (1954) , considere d the Grou p to be Lowe r Proterozoic, an d correlated i t with the Brocks Cree k Group of the Kather-ine-Darwin region . B.P . Walpole (pers.comm. ) correlates the Warramunga Group with the Brock s Creek Group , and , o n th e basis o f ag e determination s mad e on granite whic h intrudes th e Brock s Creek Group , consider s tha t both Groups are o f lower Lowe r Proterozoic age .

During 1957 , J.W . Smith collecte d fres h samples.o f granit e fro m various localitie s in th e Davenpor t and Murchison Ranges an d in the Tennan t Creek are^a. Th e age o f these sample s was determine d b y P.M. Hurley, by the potassium-argon ratio method . Th e ages o f three sample s of granit e whic h intrude the Warramunga Group are 1630, 1510 , and 1400 million years. Th e latte r two fal l int o a group of granites , whos e averag e i s 145 0 million years , an d which intrude th e sedi -ments o f th e Davenpor t an d Murchiso n Ranges . Th e age 163 0 million years i s indicativ e o f the youngest possibl e ag e o f the Warramunga Group, an d accordingly the Grou p is considere d t o be of lower Lowe r Proterozoic ag e (Hurle y et alii , 1959) .

Hatches Cree k Group

A thick , conformabl e sequenc e o f dominantl y arenaceou s rocks , whic h constitute s most o f the Davenport and Murchison Ranges, rests unconformabl y on the Warramunga Group and is regarde d a s uppe r Lowe r Proterozoic i n age (Hurle y et alii , 1959) . Par t o f this sequenc e wa s first name d th e Hatche s Cree k series by Hossfeld (1941) : h e divided i t int o three units , th e 'Top series', 'th e Hatche s Cree k series'and the'Bottom series', wit h a suggested unconformity betwee n the lowe r two units. Sulliva n (1953 ) used the nam e 'Hatches Creek ' in the sam e sense , bu t changed the classificatio n t o Group. In an unpublished paper in 1951 , Sullivan referre d to sedimentar y rock s in the Wauchope Wolfram Fiel d a s th e 'Davenpor t Range Group'; Ivana c (1954 ) referre d briefl y t o the 'Davenpor t Range Group', but he did not define it . Th e regional mappin g carried out in 1956 has

0 Thes e age s hav e not been checked by other method s an d should be accepte d with reserve .

9

shown that the sediment s of the Hatches Creek and Wauchope Wolfram Field s belon g to the on e unit; the nam e Davenport Range Group is therefor e redundant .

Hossfeld (1954 ) extende d the name'Hatches Creek* to cover both the origina l 'Hatche s Creek series ' an d th e 'To p series' i n both the Davenport and Murchison ranges; h e accepte d the classification o f 'group' and designated th e Hatche s Creek area as th e type area of the unit . How -ever h e regarde d 'Botto m series ' a s unconformabl y below the Hatche s Cree k Group. W e retain Hossfeld's Hatche s Cree k Group , bu t exten d i t to cover the 'Botto m series' becaus e o f evidence , referred t o below, to indicate tha t the 'Bottom series' i s a conformable part of the whole sequence .

The scop e o f the 195 6 survey did not permit the examinatio n of sections i n sufficien t detail t o define an d name formations, but it was recognise d tha t the sedimentar y sequenc e consiste d of severa l conformabl e formations which, i f precisely defined , woul d constitute a group. Wit h the concurrence o f th e Stratigraphi c Nomenclatur e Sub-committee , Territories Division , Geological Society o f Australia , we retai n the classificatio n o f Group, in accordance with past usage, althoug h no definite formation s within the uni t have yet been named or defined .

The rock s o f the Hatche s Cree k Group are mainly thin to medium-bedded, medium to coarse-grained, silt y silicifie d quart z sandstone . Mos t quart z grains ar e sub-rounded ; small -scale cross-beddin g i s commo n and ripple marks are abundant; tensio n joint s ar e well developed . The quart z sandston e i s usuall y eithe r pink , grey , o r blue-grey. Thes e arenites , whic h includ e some bed s an d lense s o f pebble conglomerate up to two hundred feet thick , cro p out in long, sub-parallel ridges . I n valley s betwee n th e ridges , shale , siltstone , sof t greywacke , and extrusive volcanic rock s cro p out . Th e shale , siltstone , an d greywacke ar e poorly exposed, an d complete sections o f rock s o f thes e lithologie s ar e seldo m seen . Th e extrusive rock s include both acid and intermediat e types ; usuall y the y ca n b e trace d over distances o f tens o f miles, an d they commonly maintain a fairly uniform thickness ove r suc h distances. Th e field relation s o f som e of the basi c igneou s rock s ar e not clear, an d the problem of whether they ar e extrusive rock s which are member s o f the Hatche s Creek Group or sill s which intrude the Group has no t been resolved . The basic rock s ar e discussed i n a later sectio n o f this Report.

About fou r mile s sout h o f th e souther n limit s o f the Hatche s Cree k Wolfram Fiel d there ar e outcrop s o f rock s whic h Hossfeld (1954,loc.cit. ) correlated with his Agicond i Series o f Lower Proterozoi c age . H e considered that the Hatches Creek Group rested with an angular uncon-formity o n thes e rocks , whic h h e name d th e 'Botto m series' . The y consisted o f schistos e an d sheared igneou s an d sedimentary rocks . Mappin g done during the 195 6 survey showed:

(a) Tha t th e sedimentar y rock s o f Hossfeld' s 'Botto m series ' ar e the oldest , excepting thos e o f th e Warramung a Group , expose d i n th e Davenport and Murchison Ranges . The y cro p ou t i n smal l area s onl y and they have been very strongl y sheared . Th e stron g shearin g ha s affecte d arenite s o f the Hatches Cree k Grou p whic h cro p ou t nearby , an d outsid e th e are a i t has produced schistos e rock s fro m origina l shal e an d siltston e whic h are def -initely member s of the Hatche s Creek Group;

(b) Tha t th e outcrop s o f igneou s rock s i n Hossfeld' s 'Botto m series' ar e mainly quartz-feldspar porphyr y whic h intrude s th e Hatche s Cree k Group : on e small are a o f granit e an d associate d greise n intrude s th e quartz-feldspar porphyry;

10

(c) N o evidenc e o f a n angula r unconformit y betwee n th e sediment s o f Hossfeld' s 'Bottom series ' an d his Hatche s Creek Group.

The igneou s rock s o f Hossfeld' s 'Botto m series ' undoubtedl y intrud e the Hatches Creek Grou p an d therefor e th e onl y problem is tha t of the stratigraphica l positio n o f the sheare d sedimentary rocks . I n th e absenc e o f an y angula r unconformity, they are believed t o belong to the conformabl e sequenc e o f th e Hatche s Cree k Group ; th e shearin g i s probabl y only of loca l significance.

No section s wer e measure d i n th e Hatche s Cree k Grou p during the 195 6 survey, but estimate s o f it s thicknes s wer e mad e i n tw o localities show n by section line s a-a ' an d b-b' on Plat e 1 . Bot h estimate s ar e base d o n large number s of dip angles rea d on the groun d and distances measure d fro m ai r photographs . I n sectio n a-a ' th e estimate i s 18,00 0 fee t an d in b-b' i t i s 25,00 0 feet . Th e estimat e i n a-a' i s considere d mor e reliable tha n the othe r because every significan t chang e o f dip was recorde d on this sectio n line .

The Hatche s Cree k Grou p ha s bee n intrude d b y basi c Igneou s rocks , by quartz-feldspar porpyhr y an d othe r aci d an d intermediat e igneou s rocks , and by granite. Th e basic intrusive rock s a n th e quartz-feldspa r porphyr y occu r ove r a large area . Outcrop s of acid and intermediate intrusiv e rock s generall y occup y smal l crescenti c area s i n the nose s o f folds i n the are a west o f the Hatche s Creek settlement, an d small outcrops of granite ar e found in severa l localities. Al l th e sediment s intrude d b y granite ar e stratigraphicall y lo w in the Hatches Creek Group. Th e average ag e of sample s fro m four separat e granit e bodies , determined by the potass -ium-argon rati o method , is 145 0 million years (Hurle y et al. , loc . cit.) .

In most parts o f the Davenport and Murchison Ranges, metamorphism of the Hatches Creek Grou p i s o f a lo w order ; commonl y only surface silicificatio n i s apparent . I n the south -ern par t o f th e Hatche s Cree k Wolfra m Field , however , an d for about five mile s sout h of the field's south-easter n boundary , dynamic metamorphism has converte d sandston e t o dense quartz-ite, an d shal e ha s been changed to slat e an d mica schist . I n the centra l an d northern parts o f the Hatches Cree k Wolfram Fiel d an d in severa l othe r areas , the intrusio n of basic rock s has caused , locally, sever e metasomatis m o f th e Hatche s Cree k Group ; i n thin section , albite , ollgoclase , epidote, sphene , apatite , an d chlorite ar e seen to be present .

On bot h th e Wauchop e an d th e Hatche s Creek Wolfram Fields , hornfel s I s common. On th e Wauchop e field th e formatio n of hornfel s I s due to contac t metamorphism by the intrusio n of granite ; bu t o n th e Hatche s Cree k field , evidenc e fro m thin section s indicate s tha t rocks which ar e no w biotite-sericite-quartz hornfel s ma y have been formed by metasomatlc processes .

Structure o f the Hatche s Creek Group.

The Grou p ha s bee n strongl y folde d int o numerou s basins an d domes and into syn -clines an d anticlines . Fig. 3 show s th e trend s o f majo r fold s an d faults. Th e domes and basins are roughl y oval , wit h lon g axe s rangin g fro m 1 0 to 2 0 miles i n length. Th e longest synclina l structure i s abou t 6 5 mile s lon g an d ther e ar e severa l othe r synclines , an d some anticlines , which ar e abou t 40 miles long .

The dip s ar e stee ^ i n mos t o f th e structure s o f the Davenport Range; i n the lon g synclines, dip s rang e fro m 6 0 t o vertical , an d I n some places th e beds ar e overturned by as much a s 1 0 . Th e dip s i n th e dome s and basins commonl y range from 50 t o 8 0 , but some of

1]

FI6 3 133° 30' 131T ,je'30

TECTONIC MA P

THE DAVENPOR T AN D MURCHISO N RANGE S NORTHER N TERRITOR Y SCALE

32 16 0 32 64 96 Miles

Reference

Igneous rock s

CAMBRIAN £ m s Sondover Beds 1 B 9 Proterozoic Granite

Unconfor mity 1

Proterozoic Porphyry

efi, Hatches Creek Group | U / / \ \ Basic Volconic Rocks PRECAMBRIAN Unconformity

Warramunga Group L \ v Acid Volcanic Rocks

_ - Synclinal Axis

• —p — Anticlinal Axis

/ Fault

^ ^ Trend lines t with dip of bads

Bureau of Mineral Resources, Geology & Geophysics Oct I960.

12

these structure s hav e muc h flatte r dips . I n mos t o f the are a the fol d axe s tren d roughly north-west, an d many of them have a short sigmoida l section .

In general , th e majo r fault s strik e eithe r north-eas t o r north-west . Man y trends, particularly i n mino r faults , li e betwee n those tw o dominant directions. Strik e faulting , trendin g roughly north-west, i s common.

There hav e bee n a t leas t tw o period s o f faulting ; o n air photographs of the are a several instance s o f the displacemen t o f majo r faults by younger faults ove r considerabl e horizon -tal distance s ar e clearl y visible . Evidenc e o f two periods o f faulting has been obtaine d also o n the Hatches Cree k an d Wauchop e Wolfra m Fields . O n both these field s som e o f the or e occur s i n quartz reef s whic h fil l fracture s produce d b y faulting ; smal l displacement o f som e o f the reef s is a commo n feature. Th e apparent horizontal displacemen t o n some o f the majo r fault s i s o f the order o f miles , but their vertica l displacemen t i s unknown.

Igneous Rocks

All th e igneou s rock s ar e o f Lowe r Proterozoi c age : th e granite s ar e undoubtedly the younges t o f th e intrusiv e igneou s rock s an d the averag e ag e o f the granit e bodies sample d i s 1450 millio n years (Hurle y et al. , 1959) . Th e order of intrusion i s considere d t o be: basi c rocks ; quartz-feldspar porphyr y and other acid and intermediate rocks; granite . Tha t the basic intrusive s are olde r tha n the granit e i s inferre d fro m evidence expose d i n some mine s i n the Hatche s Cree k Wolfram Field , where basic intrusive s ar e cu t by quartz vein s carryin g wolfram; th e origi n of the wolfram i s attribute d to a phase o f granitic activity, thoug h the neares t know n outcrop of granite i s about si x mile s t o the south .

Around this outcrop random stringers o f greisen extend from the granit e int o quartz-feldspar porphyry ; s o the granit e mus t be younger than the porphyry. Additiona l evidence o f thei r relative age s i s give n b y thei r attitudes . Porphyr y is foun d commonly in the core s o f domes, and simila r aci d o r intermediat e rock s occup y th e nose s o f folds; al l were probabl y emplaced, therefore, durin g an early stag e o f the folding of the sediments . Th e granite outcrops , on the othe r hand, bear no relationship t o fold structures , eithe r locall y o r regionally .

No juxtapositio n o f basi c rock s an d porphyry has been observed, and their assigne d relative age s res t o n th e probabilit y tha t th e broa d pattern of differentiation wa s fro m basic t o acid. Th e basic intrusion s cro p out in random locations, an d with one exception bea r no apparent relationship t o fol d structures . The y intrud e severa l member s of the Hatche s Cree k Group .

Thin section s o f severa l igneou s rock s fro m th e are a have been studie d by KJR. Walker; th e description s appea r i n th e Appendix , an d show the rang e in type o f igneous rocks . Both extrusiv e an d intrusiv e rock s ar e represented ; fo r example specime n DR3 8 i s clearl y a n extrusive roc k on field evidence .

The origi n o f on e typ e o f basi c roc k is i n doubt; i t crop s out intermittently ove r a large are a o f th e Davenpor t Range , an d occupie s th e sam e stratigraphica l positio n wherever i t occurs. Goo d outcrop s occu r i n th e valle y immediatel y east o f Coulter's Waterhole, which i s situated o n th e mai n roa d t o Alic e Spring s abou t 20 miles west-south-wes t o f Hatches Cree k settlement. A t thi s localit y th e uni t i s estimate d to be 2,00 0 fee t thick ; an d towards the north-western extremit y o f it s outcrop , nea r th e Devil' s Marbles , the thickness i s abou t 800 feet . In som e place s i t enclose s a thi n be d o f silicified quart z sandstone, which i s abou t 15 feet thic k and ca n b e trace d fo r severa l miles . Ther e is n o field evidenc e tha t the basalt cut s acros s th e arenites o f th e Hatche s Cree k Group , an d i t i s probabl y an extrusive roc k rather than a sill .

13

Most o f th e granit e bodies mappe d in the fiel d ar e two-mica microcline granite , but some modification s o f field description s are given in the descriptions b y K.R . Walker; fo r instance , he describe s sample s D R 4 0 an d D R 47 a s adamellite . Th e granite i n the Mosquit o Creek area differs fro m th e othe r graniti c bodie s i n that it i s porphyriti c an d contains numerou s xenoliths o f (?) basic rock .

All th e granite s exhibi t evidenc e o f stress afte r consolidation ; shearin g movements have cause d th e brecciatio n o f feldspa r crystals , th e bendin g of biotite flakes , an d undulose extinction o f quart z grains . Ivana c (1954 ) reporte d simila r minera l deformation in the granit e of the Tennan t Creek area.

The followin g age s wer e determine d b y the potassium-argon method on one sampl e of granit e fro m eac h o f fou r separat e granit e bodie s which intrude the Hatche s Cree k Group (Hurley et al. , 1959) :

Locality Age .

(a) Devil' s Marble s (6 miles 154 0 million year s

north of Wauchope)

(b) Skinne r Poun d area 132 0 " "

(c) 6 miles sout h of Hatches 148 0 " " Creek Polic e Statio n

(d) 4 miles south-wes t o f 143 0 1 1 " Supplejack Bore, Elkedra Station.

The averag e ag e o f these granite s i s i n agreemen t with that of others , obtaine d from widely-separated part s o f Centra l Australia , e.g. , Barro w Creek , an d the Jervoi s Range s and Mount Swa n i n th e Huckitt a Shee t (F53/11) ; granite s fro m these localitie s wer e date d by the same metho d and the result s recorde d by Hurley et al . (loc.cit.) .

Further determination s b y tota l roc k an d Rb/S r method s ar e necessary t o ascer -tain wha t th e K/ A age s represent . The y possibly date the las t orogen y in the are a - th e Daven-port foldin g movemen t - an d not the granit e Intrusion .

UPPER PROTEROZOI C

In severa l localitie s i n th e Davenpor t Rang e th e Hatche s Creek Group is overlain , with angular unconformity, by a formation which consists of boulder conglomerate, silt y sandstone , and siltstone . Thes e sediment s cro p out as shee t deposit s i n valleys an d also o n isolated mesa s whose topographi c leve l i s commonl y belo w tha t o f th e ridge s o f the Hatche s Cree k Group.

The thicknes s o f th e formatio n doe s no t exceed 15 0 feet an d is commonl y less than 100 feet . Th e di p o f th e bed s i s les s tha n 15 i n most places, but some dips o f 40 hav e been recorded. Th e boulder s ar e well-rounde d an d consis t o f silicifie d sandston e which is similar , in th e han d specimen , t o tha t o f th e Hatche s Cree k Group; measurement s o f the lon g axis o f boulders rang e fro m 9 t o 1 5 inches . Th e matrix of the boulder conglomerate i s usuall y laterit -ized, an d in a few areas th e matri x has been completely removed , to leave larg e number s of loose ,

14

boulders strew n o n th e surface . I n rar e instance s wher 6 this matri x has no t been strongl y lateritized i t resemble s tha t o f a tillite ; i t contain s feldspa r ^fragments, an d angular fragment s of quart z u p t o 4 mm.long. N o striations o r faceting wer e observe d o n the boulder s i n these out -crops.

The sandston e bed s o f th e formatio n ar e coarse-graine d an d cross-bedded, with a silty matrix , an d th e quart z grain s ar e commonl y well-rounded . Polygona l mu d cracks ar e common (o n falle n blocks ) an d rippl e mark s ar e numerous. Th e sandston e contain s som e bands of pebbl e conglomerate .

No fossil s hav e bee n foun d in the formatio n an d there i s n o evidence tha t i t has bee n intruded by igneous rocks . Lithologicall y the formation is ver y simila r t o the Risin g Su n Conglom-erate, whic h ha s been.name d an d describe d b y Ivana c (1954 , p.24); Croh n et al . (1959 , unpubl.) also describ e th e Risin g Su n Conglomerat e an d record that i t ha s no t been intrude d by any of the igneous rock s o f the Tennan t Creek area .

The formatio n ma y possibl y b e o f lowe r Middl e Cambria n age, a s bed s o f this ag e crop ou t aroun d th e margin s o f th e Davenpor t Range ; the y wil l b e discussed i n a later section , but i t migh t b e note d her e tha t th e Cambria n sediments hav e no t been folded an d that, althoug h they commonl y contai n a basa l conglomerate , ther e ar e numerou s dissimilaritie s betwee n thes e conglomerates an d those o f the bed s unde r discussion .

Another possibilit y i s tha t th e beds ar e o f fluvio-glacia l origin , bu t there i s n o def-inite evidenc e t o suppor t this . I n Centra l Australia , glacial deposit s o f Upper Proterozoic ag e have bee n reporte d fro m th e Tobermor y an d Huckitt a area s (Noakes , 1956) and from Ellery' s Creek i n th e Wester n MacDonnel l Range s (Prichar d & Quinlan , pers. comm. ) Th e sequenc e in th e Davenpor t Rang e ma y perhap s recor d thi s Uppe r Proterozoic glaciation . Th e balance of evidence seem s t o be in favour o f an Upper Proterozoic age , bu t no correlation wit h known Upper Proterozoic rock s elsewher e i s made .

CAMBRIAN

Cambrian sediment s cro p ou t o n th e north-eastern , eastern , south-eastern , an d southern fringe s o f the Davenpor t Range an d also o n the plain s nort h and north-east o f the Range. While th e part y wa s i n th e field , we t ga s was encountere d i n a bore o n Ammaroo Station . Th e bore wa s drille d int o Cambria n sediment s whic h ar e highe r stratigraphicall y tha n the beds ex -posed o n the souther n fring e o f the Davenpor t Range.

During th e 195 6 survey , Cambria n sediment s wer e mappe d i n reconnaissanc e detail only . Fossil s wer e collecte d fro m numerou s localitie s an d were late r examine d by A .A. Opik an d Joyce Gilbert-Tomlinso n of the Burea u of Mineral Resources.

The firs t recor d of Cambria n sediments i n the are a was provide d by A .A. Davidson , who, i n th e cours e o f hi s prospectin g expeditio n o f 1898-99 , collecte d fossil s fro m a localit y 'forty-five mile s south-eas t fro m Elkedr a Station ' (thi s refer s t o the ol d Elkedra homestead). From th e specimen s collecte d b y Davidson, Etheridge (1902 ) described Pageti a significan s (Eth. ) and Peronopsis elkedraensis .

In th e are a mapped , Cambria n sediment s cro p ou t i n isolated mesa s an d in smal l plateaux. Th e sediment s rest , wit h a n angula r unconformiy , on rocks o f the Hatche s Creek Group an d o n igneou s rock s whic h intrud e tha t Group . Th e Cambrian sequence ma y be divide d into tw o conformable units :

15

(a) a basal uni t o f conglomerat e an d sandstone ; (b) a unit o f shale , chert , an d limestone .

No measurement s o f tota l thicknes s wer e made , bu t i t i s estimate d tha t this would not excee d 250 feet .

ft

Opik (1956 ) propose d th e informa l nam e 'Sandove r Beds ' fo r a sequence o f lowe r Middle Cambria n sediment s whic h cro p ou t immediatel y nort h o f the Sandove r River , about 25 miles sout h o f th e souther n margi n o f th e Davenpor t Range. Th e Sandover Beds ar e a contin -uation o f th e Cambria n sediment s o n th e souther n margi n of the Davenpor t Range; becaus e th e mapping in 195 6 was reconnaissanc e only , formatio n names will no t be given t o (a ) and (b) outlined above; th e nam e 'Sandove r Beds ' i s extende d t o include thes e units .

In uni t (a ) n o fossil s wer e found . Th e basal conglomerat e differ s fro m that o f the ?Upper Proterozoi c sediment s i n that cobbles an d boulders o f the Cambria n sequence ar e angula r and ar e compose d o f al l roc k type s o n which the sequenc e rest s i n that vicinity . I n some place s large angula r block s o f th e underlyin g roc k types ar e incorporate d i n the Cambria n sequence. A representative sectio n o f uni t (a ) wa s measure d i n a mesa 7 miles nort h of Supplejac k Bore on Elkedra Station. Her e the sequence , i n descending order , consist s of :

Top of mesa ;

7 fee t

10 "

1 "

1 " 2 " 3 " 1 " 2 "

10 "

37 fee t

The sectio n unconformabl y overlies aci d volcanic rock s o f Lowe r Proterozoic age .

Unit (b ) carrie s a n abundan t an d well-preserve d faun a whic h include s trilobites , brachiopods, an d hyolithids . Th e faun a clearl y indicat e a lower Middl e Cambrian age (6pik & Gilbert-Tomlinson, pers. comm.) .

6pik (pers.comm. ) consider s tha t th e fossiliferou s Cambria n outcrops o n the east -ern an d north-easter n fringe s o f th e Davenpor t Rang e ar e a correlate, an d probably a former extension, o f th e Gu m Ridg e Formatio n (Ivanac , 1954) . I n accordance wit h this opinion tw o seq -uences o f lowe r Middl e Cambria n sediment s ar e show n o n Plate 1 - th e Gu m Ridge Formation and th e younge r Sandove r Beds . I n ou r opinion , there ar e n o lithological differences , i n the area mapped , betwee n th e Gum Ridge Formatio n and the Sandove r Beds , bu t slightl y olde r trilob-ites hav e been foun d i n the norther n area .

quartz sandstone , coarse-grained , cross-bedded , brown , wit h angula r pebbles o f quartz;

quartz sandstone , brown , medium-grained , silty , wit h som e thi n pebbl e bands;

pebble conglomerate ; quartz sandstone , brown , coarse-grained, laminated ; cobble conglomerate ; quartz sandstone , brown , coarse-grained, thin-bedded ; pebble conglomerate ; quartz sandstone , brown , medium-grained, cross-laminated , silty ; boulder conglomerate ; th e boulder s ar e angula r an d consis t o f quartz, quartz sandstone , an d acid volcanic rocks . Th e size o f the boulder s range s to 9 inches .

16

In th e are a mappe d ther e ar e n o sign s o f tectoni c disturbanc e i n either th e Gum Ridge Formatio n o r th e Sandove r Beds . 6pi k (1956,p.35) ha s recorde d weak fault movement s i n the Sandove r Beds a t a locality a few miles sout h of the are a unde r discussion .

? TERTIAR Y

A porou s pebbl y limeston e whic h i s believe d t o be of Tertiary age crop s ou t in sev -eral isolate d localitie s i n th e are a mapped . Th e most extensiv e are a of outcro p i s nea r th e north-western en d o f th e Davenpor t Range . I n additio n there ar e smal l outcrop s nea r Kurundi Station homestead, eas t o f Macro b Bore on Elkedra Station, an d in the Hatche s Cree k area. Evid -ence fro m wate r bore s indicate s tha t simila r rock s underli e san d and alluvium i n the Warrabr i area, an d similar roc k was encountere d i n a well a t Murray Downs Station homestead.

The rock s commonl y crop out poorly; the y ar e white o r grey an d on air photographs they sho w a pattern of scattere d whit e dots . Numerou s flint nodule s occu r in the sediments . Th e thickness o f th e sequenc e i s unknown ; abou t 40 feet i s expose d i n the are a on the north-wester n end o f th e Davenpor t Rang e an d a thicknes s o f 5 0 feet ha s bee n reported in the wel l a t Murra y Downs homestead .

No fossil s hav e bee n foun d i n th e sequence . Noake s & Traves (1954 ) considere d that sediment s o f simila r litholog y i n the Tennant Creek area an d on the Barkly Tablelands were o f Tertiary ag e an d th e sequenc e i n th e Davenpor t Rang e are a i s als o believed t o be o f this age .

ECONOMIC GEOLOG Y

The mos t importan t ore s produce d fro m th e are a ar e those o f tungsten. Smal l deposits o f copper , lead , an d gol d hav e bee n worke d by prospectors, an d there i s on e uranium prospect.

Tungsten

Ores o f tungste n hav e bee n mine d o n th e Hatche s Creek , Wauchope, an d Mosquito Creek fields , an d on e smal l deposi t ha s bee n worked in a quartz vein in granite abou t two mile s south o f Supplejac k Bor e o n Elkedr a Station . Anothe r small prospect occur s nea r Epenarra Station homestead .

The Hatche s Cree k fiel d i s th e larges t o f th e three minin g fields. Th e main ore produced i s wolfram , bu t scheelit e ha s been found in some prospects; bismut h and copper occu r in th e or e i n severa l mines . Th e Hatche s Cree k Wolfram Fiel d was mappe d in detail i n 1956 and the result s ar e being published (Ryan , 1961),

The Wauchop e Wolfram Fiel d rank s secon d to the Hatche s Cree k field i n production. Sullivan (1952 ) reporte d o n th e geolog y an d production of this field; a brief inspectio n wa s made by the author s i n 1956. Wolfra m is mined from narrow quartz veins whos e dip s ar e generall y low . The quart z vein s ar e commonl y concordan t i n bot h di p and strike wit h the beds o f the Hatche s Creek Grou p i n whic h the y occur . Th e wolfra m mines ar e located o n the souther n limb of a large anticlin e whic h pitches i n an easterly direction . Th e nearest outcroppin g granite i s a small body abou t 2 | mile s nort h of the wolfram field (A.G.G.S.N.A. , 1941) ; i n the mine s ther e ar e beds of hornfel s produce d by contact metamorphis m of the Hatche s Creek Group by granite intrusives .

17

The Mosquit o Cree k Wolfra m Fiel d was discovere d i n 1951 : brie f inspection s wer e made b y Joklik & Tomich (1951) and Bell (1953). Som e smal l ric h pockets o f wolfram an d scheelit e have bee n mined. Th e or e occur s i n narrow quartz veins whic h occupy shear s i n granite . Som e scheelite ha s bee n obtained from the soi l adjacen t to severa l o f the quartz veins. Ther e was very little minin g activit y o n this fiel d i n 1956 , and at present (1961 ) ther e i s none .

Uranium

In 1955 , secondary uranium minerals wer e discovere d abou t seven mile s south-wes t of th e wolfra m working s a t Mosquit o Creek ; th e uraniu m deposit wa s inspecte d b y Lor d (1955) . The prospec t i s locate d i n a shear in rocks o f the Warramunga Group ; th e surfac e exten t i s small , but during 195 6 the lesse e san k two shaft s t o test the depth of the prospect .

The regiona l geologica l part y selecte d thre e area s fo r testing by airborne scintillo -graph, and severa l radioactiv e anomalie s wer e detecte d fro m th e aircraf t (Livingstone , 1957) ; the result s wer e release d t o the public upon completion of the airborn e survey . Som e of the anom-alies wer e inspecte d b y the regiona l geologica l part y and by a car-borne surve y from the Geophy-sical Branc h of the tBureau. N o worthwhile deposits o f radioactive mineral s were discovere d dur-ing thes e groun d inspections , no r were an y found by prospectors who examined som e o f the other anomalies.

18

T A B L E 1

AGE LITHOLOGY TOPOGRAPHY IGNEOUS A C T I V I T Y ,

FOSSILS, E T C.

Quarternary

Tert iary

UNCONFORMITY

Middle

Cambrian

? Uppe r Proterozoi c

• UNCONFORMIT Y

UNCONFORMITY

Lower

Proterozoic

Hatches Cree k Group

- UNCONFORMIT Y

Lower

Proterozoic Warramunga

Group

Sand, alluviu m

Limestone

Thin-bedded, c r o s s -bedded, ripple-marked , medium an d coars e grained, sub-angula r quartzite an d sandstone ; shale, greywacke , pebble conglomerate , siltstone, interbedde d acid volcanics .

Quartz sandstone ,

greywacke, shale ,

siltstone

Good supplie s o f

underground wate r

Quartz sandstone , conglom - Mesas an d lo w Brachiopods, erate, shale , l imestone , rounded hill s Tri lobites , chert. Hyolithids.

Conglomerate, sandston e Low outcrop s i n valleys, lo w mesas

Long

parallel

ridges

separated

by fla t val leys,

Quartz-feldspar porphyry an d aci d intrusives. Basic stock s an d intrusions

Basic s i l l ?

Basic flow ?

Ore deposits .

End o f orogeny .

Folding i n progres s .

Orogeny begin s

Deposited i n Daven -port Geosyncline ,

Low pinnacles , Low m e s a s .

STRATIGRAPHY O F TH E DAVENPORT RANG E ARE A

LIST OF REFERENCE S

A.G.G.S.N.A., 194 1

BELL, A.D.M. , 195 3

BROWN, H.Y.L, , 189 5

BROWN, H.Y.L. , 189 6

BROWN, H.Y.L. , 190 3

CROHN, P.W. , OLDER - 195 9 SHAW, W. , and RYAN , G.R.,

DAVID, T.W.E.(ed . 195 0 BROWNE, W.R.) ,

DAVIDSON, A.A. , 190 5

HOSSFELD, P.S. , 195 4

HURLEY, P.M . an d 195 9 others

IVANAC, J.F. , 195 4

JOKLIK, G.F. , an d 195 1 TOMICH, S.A. ,

LANGRON, W.J. , 195 7

LIVINGSTONE, D.F. , 195 7

Report fo r th e perio d ende d 31s t November , 1940 . Aer . Surv. N . Aust.

Preliminary repor t o n th e Mosquit o Cree k Tungste n Field N.T . Bur . Min.Resour.AustJlec.1953/1 8 (unpubl.) .

Report o f Norther n Territor y explorations . S .Aust.pari. Pap. N.82.

Report o f Norther n Territor y Explorations . S»Aust.parl . Pap. N.127.

Report o n countr y recentl y examine d i n th e Davenpor t and Murchison Ranges . S .Aust .pari .Pap N.27 .

The geolog y o f th e Tennan t Cree k gol d an d coppe r field. Bur.MlnJElesour.Aust . Rec . 1959/4 9 (unpubl. )

THE GEOLOGY OF THE COMMONWEALTH OF AUSTRAL -IA. London , Arnold.

Journal o f exploration s i n Centra l Australia , 1898-1900. S .Aust .pari .P ap .N.27.

Stratigraphy an d structur e o f th e Norther n Territor y o f Australia. Tran s .Roy .Soc.S .Aust.,77,103-161.

Geochronology o f Proterozoi c granite s i n th e Norther n Territory, Australia . U.S.Atom . Energ y Comm . Rep . NYO-3940, 122-149 .

The geolog y and mineral deposits of the Tennant C reek Gold -field, Norther n Territory . Bur.Min.Resour.Aust.Bull . 22 .

Report o n a n inspectio n o f th e Mosquit o Creek , N.T. , Wolfram Field . Bur.Min.Resour.Aust.Rec . 1951/5 3 (un -publ.).

Carborne radiometri c survey s i n th e Davenpor t Rang e area, N.T. , 1956. Bur.Minjiesour.Aust.Rec. 1957/5 8 (un -publ.).

Airborne scintillograp h surve y i n the Mosquito Creek reg-ion, Norther n Territory . Bur.Min.Resour.Aust.Rec . 1957/ 80 (unpubl.) .

20

LORD, J.H. , 195 5

MURRAY, W.R. , 190 7

NOAKES, L.C. , an d 195 4 TRAVES, D.M. ,

NOAKES, L.C. , 195 6

OLIVER, T.G. , 191 6

OPIK, A.A. , 195 6

OWEN, H.B. , 194 2

RYAN, G.R. , 196 1

SULLIVAN, C.J. , 195 1

SULLIVAN, C.J. , 195 2

Report o n a n inspectio n o f a uraniu m prospec t nea r Mosquito Creek , Norther n Territory . Bur.MinJlesour . Aust.Rec.1955/62 (unpubl.) .

JOURNAL (WIT H PLANS) OF THE GOVERNMENT PROS-PECTING EXPEDITIO N T O TH E BUXTON AND DAVEN-PORT RANGES , NORTHER N TERRITORY . Adelaide , S.Aust.Govt Printer .

Outline o f th e geolog y o f th e Barkl y Region . J n Surve y of th e Barkl y Regio n 1947-48 . Sc i .ind.Res.Org.,Melb., Land Res. Ser.No.3,34-41.

Upper Proterozoi c an d Sub-Cambrian rock s i n Australia . In E l Sistem a Cambrico , su Paleografi a y el Problem a d e su base , 2 , 213-238 . 20th int.geol.Cong. , Mexico .

Report o f inspectio n o n Hatche s Cree k Wolfra m mines . Bull.N.Terr.Aust. 21

Cambrian geolog y o f th e Norther n Territory . I n El Sist -ema Cambrico , s u Paleografi a y e l problem a d e S u base , 2, 25-54,20t h int.geol.Cong,, Mexico ,

Report o n th e Tennan t Cree k Goldfield . Geo!.Br.,Dep.Int . Aust .(unpubl.)

The Hatche s Cree k Wolfra m Field . Bur.Minjtesour . Aust.Bull. 6 (i n press )

Hatches Cree k Wolfra m Field .Bur .Min Jtesour .Aust .Rec, 1951/35(unpubl,),

Wauchope Wolfra m Field , Norther n Territory.Bu r .Min. Resour.Aust.Bull.4

21

APPENDIX

PETROGRAPHIC DESCRIPTION S

by

KJt. WALKE R

DR26: Granophyri c quartz-feldspar porphyry.

Hand Specimen: Th e rock is red-brown and has a massive igneou s appearanc e an d a sub-conchoidai fracture. I t i s porphyritic ; phenocryst s o f pink feldspar an d quartz are evenly distribute d i n the aphanitic groundmass . I n a fresh surface minute mica flakes flec k the groundmass . Th e weathered surface i s iron-staine d an d forms a yellow-brown crust o n the rock.

Thin Section : Th e roc k i s porphyritic , glomeroporphyritic , an d granophyric . Phenocryst s o f plagioclase an d quart z ar e se t i n a delicat e feather y granophyri c base. Th e quartz phenocrysts are generall y corrode d an d measur e u p t o 1. 5 mm. , and those o f plagioclase ar e subhedra l or euhedral an d measur e u p t o 2 mm.; the y ar e i n optical continuit y with their correspondin g com-ponent i n th e surroundin g intergrowth ; on e o f th e plagioclase crystal s i s strongl y corroded. The feldspa r o f the intergrowth is light brown; needles o r ray s o f quartz which form feathery inter -growth wit h i t ar e u p t o 0. 3 mm . long . Numerou s spherulites u p to 0,5 mm. across ar e i n the granophyric groundmass . Throughou t ar e smal l opaqu e iro n mineral grain s an d flecks o f white mica. Rar e small zirco n and apatite grain s occu r throughout . Th e plagioclase i n the phenocryst s is oligoclas e an d i s twinne d mostl y accordin g t o th e albit e law . Phenocryst s ar e fairly fresh , though flecked with sericite . Th e feldspar i n the bas e has a light brow n clouding.

DR34: Metamorphose d dolerite.

Hand Specimen: Th e dark gre y massive basic igneous roc k is medium-graine d and consists main -ly o f dark green hornblende an d cream plagioclase. Fin e pyrite grain s occu r throughout.

Thin section : Th e thi n sectio n i s blastophitic , an d consists almos t entirely o f roughl y equal amounts o f plagioclas e an d uralitize d pyroxene . Subordinat e amount s of hornblende, biotite, quartz, an d opaque iron mineral ar e present. Th e feldspar lath s ar e from 1 to 3 mm. long and the ferromagnesian minera l grain s rang e betwee n 1 an d 4 mm . across. Th e plagioclase crystal s are euhedra l an d lath-shaped, o r tabular . Bot h simple an d complex twins ar e commo n and meas-urements o n two crystals wit h albite-Carlsbad twins indicat e composition s o f A b^ ^ U Q g an( ^ An . Man y crystal s ar e zone d an d undulos e extinctio n i s als o common . Alteration , mostly of

66 adjacent ferromagnesia n minerals , resulte d in the development of uralitic amphibol e along feldspar cleavages. Th e ferromagnesia n grain s ar e mostl y core s o f pyroxene within uralitic amphibol e -or ar e origina l pyroxen e rimme d wit h amphibole . However , alteration to amphibole has als o occurred alon g cleavages . Thes e grain s ar e subhedra l or xenomorphic, as ar e the fe w grains of hornblende tha t occu r wher e alteratio n ha s bee n slightl y mor e extensive. I n the origina l pyrox-ene, an d in the partly uralitized grains , relict vschiller structure s ca n be seen . Th e small inclus -ions formin g thi s structur e appea r to be altere d to amphibole . O f the minor constituents, opaqu e iron minera l i s th e mos t abundant , an d grain s measur e from 0.5 to 2 mm. Biotit e flakes , 0. 2 to 1 mm. across are also evenly distributed throughout. Quart z form s irregular interstitia l grains .

The roc k i s a n autometamorphose d dolerite , o r a dolerite tha t has undergone ver y

22

t

low-grade metamorphism . Th e latte r alternativ e i s supporte d b y the undulos e extinctio n an d slight granulatio n o f wav y feldspa r grains , an d als o b y the development o f amphibole in their cleavages an d cracks . However , feldspa r alteratio n involve s n o more than sligh t fleckin g wit h sericite; feldspa r ha s probably changed little fro m its primar y composition.

DR40: Adamellite .

Hand Specimen: Th e rock is fine-grained and granitic; i t i s coloure d pink by the feldspar . Spars e phenocrysts o f feldspa r measur e u p t o 1 0 mm . Feldspar , quartz, biotite, an d muscovite ca n be identified. Quart z i s translucen t grey , an d the micaceou s mineral s ar e widespread, forming , in places, clots .

Thin section : Th e roc k i s anhedra l granular . I t consists mostl y of microcline, plagioclase , quartz, biotite , an d muscovite . Th e accessor y mineral s ar e apatit e an d an epidote mineral . Grain siz e range s fro m les s tha n 1 mm . u p to 3 mm.; generally , th e microcline grain s ar e larger tha n those o f quartz , and the muscovit e flakes ar e considerabl y large r than those o f biotite . Quartz mostl y form s irregula r interstitia l grain s fro m 0. 5 t o 2 mm. across; i t show s stron g undulose extinctio n an d partia l granulation . Plagioclas e i s th e mos t abundan t feldspar; mos t grains ar e xenomorphi c an d turbid brown; the y contain indistinc t albit e twi n lamellae which may be flexe d an d sho w strain . Th e composition of the plagioclase canno t be directly determined , but as it s refractiv e inde x i s slightl y greate r tha n tha t of Canada balsam, i t i s probabl y oligoclase. Microcline i s slightl y perthiti c an d form s xenomorphi c grain s tha t sho w fairly coars e gridiro n twinning, an d onl y sligh t alteration . Flake s o f biotit e averag e abou t 0.5 mm. in size , an d are pleochroic fro m dar k greenis h brow n t o buff . Muc h of the biotit e i s strun g out as i f occupyin g fractures. Pleochroi c haloe s ar e common , and granular epidote occur s i n close associatio n wit h groups o f biotit e flakes . Th e muscovite almos t everywhere show s sign s o f distortion . A micro-metric analysi s b y poin t counte r o f th e thi n sectio n show s that i t i s compose d of 31.9 % quartz, 29.5% plagioclase, 27.1 % microcline perthite , 6.9 % muscovite, 4.7 % biotite.

The roc k i s a n adamellite , bu t i t ha s certai n affinitie s wit h a n alkali granit e i n it s abundance o f muscovite .

DR.41. Silicifie d albit e porphyry.

Hand Specimen : Th e roc k i s mauve-brow n an d massive, an d breaks with a conchoidal fracture . Small feldspa r phenocryst s ca n b e recognise d i n the aphaniti c groundmass . Th e weathered sur -face i s pitte d an d iron-stained.

Thin Section : Subhedra l feldspar phenocryst s ar e evenly distributed i n an incipiently recrystall -ized bas e o f quart z an d feldspar . Smal l bundle s o f biotite flakes , u p to 0.2 mm. across, ar e evenly distribute d throughou t th e base . Th e phenocrysts rang e i n siz e fro m 0. 5 to 2. 5 mm. Th e groundmass i s silicifie d an d contain s irregula r quart z grain s tha t averag e 0.15 mm, across. Aggregates o f quart z for m patche s u p t o 1mm . across; the y are probably recrystallized quartz phenocrysts. Th e feldspar phenocrysts ar e albite , a s their refractiv e inde x is belo w that o f Can -ada balsam; the y ar e twinned accordin g to the albit e law. Accessor y minerals ar e chlorite , horn-blende, apatite , zircon , sphene , an d opaqu e iron mineral. Th e iron mineral i s fairl y widely dis -tributed throughout in this section .

23

DR42. Silicifie d dacite .

Hand Specimen . Th e roc k i s dar k gre y an d massive, an d breaks with a conchoidal fractur e to expose flesh-coloure d feldspa r phenocryst s (u p t o 2 mm.) i n a dark aphaniti c groundmass . Th e weathered surfac e i s buff-gree n an d spotted with slightl y weathered feldspa r crystals .

Thin Section : Th e textur e i s porphyritic ; mos t phenocrysts ar e plagioclase . Plagioclas e crys -tals als o for m glomeroporphyriti c patches . On e group of xenomorphic plagioclase grain s form s a rounde d mosaic , an d ma y therefor e hav e bee n a rock fragment caught up in the magma. Th e groundmass i s finel y crystallin e an d consists mainl y of quartz and possibly som e plagioclase. I t comprises quart z with abundan t sericite an d some biotite. an d the averag e grainsiz e o f the irreg -ular quart z grain s i s 0.1 5 mm. Biotite , however , als o form s bundles o f criss-cros s flake s whic h may pseudomorp h origina l ferromagnesia n mineral s o r i s strun g out in trains formin g an irreg-ular network . Accessor y mineral s ar e calcite , opaqu e iro n mineral, chlorite , sphene , apatite , and zircon . Mos t phenocryst s ar e euhedra l an d measur e up to 3 mm. Th e plagioclase ha s a positive opti c axia l angl e an d a refractiv e inde x slightl y greate r tha n that o f Canad a balsam; so i t i s albite-oligoclase . I t show s variabl e sericitization . Th e phenocrysts for m 20 % of the thin sectio n an d biotite 10% . Th e remainder i s groundmass .

DR43: Metadacite .

Hand Specimen . Th e weathered surfac e i s fles h pin k and spotted with feldspar phenocrysts . Th e rock break s wit h a sub-conchoida l fractur e an d expose s a red-brown surface showin g feldspar phenocrysts i n a n aphanitic groundmass . A few quartz phenocrysts ca n be recognised. Th e feld-spar phenocryst s measur e up to 3 mm.

Thin section : Th e roc k is porphyritic ; mos t phenocrysts ar e plagioclase an d the remainde r are quartz. Thos e o f plagioclas e measur e u p t o 2, 5 mm, and those o f quartz up to 1 mm, across. The phenocryst s ar e se t i n a finely crystallin e groundmas s which appear s somewha t feathery, a s much o f th e intergrow n quart z an d alkali-feldspa r form s narrow and branched grains. Althoug h the thi n sectio n i s noncrystalline , resolutio n o f crysta l margin s i s difficult , eve n under high" power. Fin e whit e mic a flake s ar e scattere d throughou t the groundmass . Th e plagioclase i s albite-oligoclase; i t i s mor e or less evenl y flecke d with minute flakes o f sericite . Quart z pheno-crysts ar e corroded , hav e pseudo-inclusions, an d show undulose extinction . Accessor y minerals are zircon , opaque iron mineral , biotite , an d sericite. Th e iron mineral i s widespread . Estimat e of minera l percentage s ca n onl y b e roughl y made. Plagioclas e phenocryst s for m 10 % and those of quart z 5% and of biotite 3%. Th e groundmass forms 10 % and quartz and feldspar eac h 35 % of the rock. Th e accessory mineral s accoun t for the las t 2%.

DR44: Metadacite .

Hand Specimen : Th e rust-staine d an d flesh-coloure d weathere d surfac e contain s weathere d feldspar phenocrysts ; th e roc k break s wit h a conchoida l fractur e an d exposes a dark brown surface containin g numerou s pin k feldspa r phenocryst s tha t measure up to 4 mm. across. The y occur i n an aphanitic groundmas s with evenly distribute d smal l biotite flakes .

Thin Section : Th e roc k i s porphyritic . Th e phenocrysts ar e euhedral oligoclase crystal s tha t measure u p t o 3 mm . Biotit e phenocryst s ar e widespread an d smaller; the y form singl e flake s or ar e groupe d togethe r i n bundles . Th e groundmas s consists o f finely crystallin e quart z and feldspar, an d contain s numerou s smal l biotit e an d chlorit e flakes . Th e intergrowth o f quartz

24

and feldspar grain s tend s t o be feathery. However , complete resolutio n o f al l grain s i n the ground-mass i s difficult . Accessor y mineral s ar e zircon , sphene , epidote, hornblende , calcite, an d apatite. Opaqu e iro n minera l i s widel y distribute d throughout ; som e grain s measur e up to 0.5 mm. bu t mos t ar e muc h smaller . Mos t biotit e flake s ar e pleochroic fro m light golden-brow n to dark green-brown . Alteratio n to chlorit e alongth e cleavages i s common . Th e chlorite als o form s individual flake s tha t ar e strongl y pleochroic fro m pale to rich lettuce-green .

DR47: Adamellite .

Hand Specimen : Th e roc k consist s o f pin k feldspar , translucent quartz , and muscovite; biotit e can b e recognise d also . I t i s partl y weathere d an d inclined to disintegrate int o grain s o f it s component minerals . I t is medium-grained ; grain s averag e abou t 5 mm.

Thin Section : Th e roc k i s euhedra l granula r and consists mainl y of quartz , plagioclase, micro -cline-perthite, muscovite , an d biotite . Man y o f th e grain s ar e fractured an d partly granulated; the grainsiz e range s fro m 1 t o 5 mm . Secondar y minerals ar e sericit e an d chlorite. Quart z grains measur e u p t o 5 mm.; the y ar e fracture d an d show undulose extinction . Moreover , part-ial granulatio n ha s resulte d i n som e o f the m bein g traversed by feathery fractures . Th e feld-spar i s mostl y microcline-perthit e an d perthiti c microcline ; grain s rang e up to 5 mm. The y show typica l gridiro n twinnin g an d well-develope d cleavage . Man y irregular crack s travers e them, som e o f whic h ar e occupie d b y biotite . Th e plagioclase i s oligoclase ; i t generall y con -tains numerou s albite twin lamellae, bent in many grains. Muscovit e flakes measur e up to 5 mm. but man y ar e smaller . A s the y ar e strongl y cleave d i t ca n be seen that they ar e flexed . Biotit e has grow n along some cleavages ; som e o f it i s altere d to chlorite ; opaqu e iron mineral i s assoc -iated wit h i t i n some places. Bot h biotite an d chlorite contai n numerous smal l pleochroic haloes . The biotit e i s pleochroi c fro m pal e brow n t o green-brown . Th e thin section consists , b y visual estimate, o f 35 % quartz, 30% microcline-perthite, 25 % plagioclase, 7 % muscovite an d 3% biotite.

DR51: Metabasalt .

Hand Specimen ; Th e roc k is massiv e an d appears to be basic igneous. * I t is s o fine-graine d tha t individual mineral s canno t be readily identified . Facet s o f ferromagnesian minerals an d feldspar can be recognised with difficulty. Th e rock has a n iron-stained weathere d surface .

Thin Section : Th e thi n sectio n ha s a n intergranula r texture an d contains glomeroporphyriti c patches o f feldspa r laths . I t consist s mainl y o f plagioclase, uralitic amphibole , epidote, and chlorite. Accessor y mineral s ar e opaqu e iro n mineral , sphene , quartz , and prehnite. Mos t plagioclase lath s ar e abou t 0. 5 mm . long , bu t lath s i n the glomeroporphyriti c patches, an d also some individua l laths , attai n 1 mm . Mos t interbedde d uralitic amphibol e grains ar e less tha n 0.2 mm , across , bu t a fe w pseudomorph s reac h 1 mm. Th e plagioclase i s oligoclase-andesine ; laths ar e euhedra l o r subhedral . Muc h o f the twinning preserved i s accordin g to the albit e law . Alteration i s t o epidote ; mos t lath s contai n smal l grain s o f this mineral an d show undulose extinction. Th e coloure d mineral s ar e uraliti c amphibole , epidote , an d chlorite. Thes e occu r interstitially, but , a s mentioned , epidot e i s include d within many plagioclase laths . Th e uralitic amphibole tend s t o b e fibrous , pale , an d onl y slightl y pleochroic . Uralitization o f the origina l ferromagnesian minerals ha s resulte d i n the formatio n of som e quart z as a by-product.

The rock is a fine-grained basal t or dolerite which has undergon e low-grade region -al metamorphism . I t is probabl y best calle d a metabasalt. Th e original feldspa r would have been more basic ; lim e with som e o f the magnesi a from origina l ferromagnesia n minerals ha s gon e to make u p epidot e an d chlorite . Muc h o f th e opaqu e iron mineral has been converted to sphene .

25

r

The stres s resultin g fro m reconstitutio n wa s no t sufficien t t o align mineral grains ; bu t stres s is evidence d i n the feldspar lath s b y their undulos e extinction , fracturing , an d bent twin lamellae ,

DR52: Dolerite .

Hand Specimen : Th e roc k i s fine-graine d an d of basaltic appearance . I t is massive , an d breaks with a sub-conchoida l fractur e to expose a medium-grey surface. It s weathered surfac e i s iron -stained.

Thin Section : Th e thin sectio n consist s essentiall y o f altere d feldspa r lath s an d interstitial epid -ote, uraliti c amphibole , an d chlorite . Original pyroxen e form s cores wit h uralitic amphibole . There ar e a numbe r o f penninite-fille d cavitie s wit h euhedra l inclusion s o f epidote. Th e laths range u p t o 2 mm . lon g and most interstitia l grain s rarel y exceed 1 mm, across an d have indef -inite grai n margins . Accessor y mineral s ar e opaque iron mineral , sphene , calcite , apatite , and quartz. Mos t o f the feldspa r laths ar e pitted with smal l epidot e an d chlorite inclusions . Muc h of the twinnin g ha s becom e indefinite ; th e refractiv e inde x of the feldspa r indicate s tha t i t i s prob -ably aci d oligoclase . Mos t o f the original ferromagnesia n mineral s hav e been altered to uralite; chlorite i s anothe r produc t of alteration and , with epidote, also form s the cavit y fillings . Opaqu e iron minera l grain s averag e abou t 0.2 mm. across an d are evenly distribute d throughout ; skelet -al grain s sugges t tha t th e minera l i s ilmenite . Th e rock is slightl y metamorphose d or auto -metamorphosed.

DR107: Siltstone .

Hand Specimen : Th e roc k i s a buff-gre y siltstone . It s weathered surfac e i s dar k rusty-brown. The fractur e o f the roc k is partl y controlled by the poor cleavage . Grai n is to o fine fo r individual minerals t o be identified .

Thin Section : Th e thi n sectio n i s finel y micaceou s an d has a poor schistosity . Th e lineation o f mica flakes ma y parallel origina l bedding-planes ; numerou s quartz and feldspar grain s ar e even -ly distribute d throughout . Thes e measur e u p t o 0. 1 mm., whereas th e mic a flakes ar e much smaller. Feldspa r i s a n important component. Gridiro n twinning indicate s tha t som e opaqu e iron mineral grain s ar e widespread ; thes e includ e som e magnetit e idioblast s (0. 1 mm. diameter). Accessory mineral s ar e gree n tourmaline , apatite, hornblende , leucoxene, an d epidote. Th e thin section i s cu t by a siliceous vei n 0.1 mm. wide.

DR131: Oligoclas e basalt .

Hand Specimen : Th e roc k i s massiv e an d has a rusty-brown weathered surfac e i n which cream weathered plagioclas e crystal s u p t o 8 mm . acros s ca n be seen . Fractur e i s irregula r an d the fresh surfac e i s green-grey . Withi n th e gre y fin e groundmass , cream plagioclase phenocryst s and gree n epidote grain s ca n be identified .

Thin Section : Th e thi n sectio n i s tha t o f a porphyritic basic igneou s roc k with numerous amyg-dules. Th e plagioclas e phenocryst s ar e euhedra l an d u p to 3mm. across; the y are se t i n a groundmass o f feldspa r microlite s an d fin e actinoliti c needles . Glomeroporphyriti c patches o f feldspar als o occur . Th e amygdule s dominat e th e texture an d consist o f epidote with or without quartz o r chlorite ; the y measur e up to 5 mm. in diameter, an d have layered structures : tha t is , some hav e a core o f chlorit e bordere d by a shel l o f epidote. Fin e opaqu e iron mineral grain s ar e scattered throughou t th e base. ^ Accessory mineral s ar e calcit e an d biotite. Calcit e occurs i n amygdules an d i n feldspar . Th e plagioclase i s oligoclase , an d that i n phenocrysts contain s albit e

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lamellae, a s wel l a s comple x twin sub-individuals . Crystal s have a light brown clouding.

The roc k i s a porphyriti c an d amygdaloida l oligoclas e basal t whose alteratio n i s deuteric o r extremely low-grad e regional .

DR133: Dolerite .

Hand Specimen : Th e roc k break s wit h a n uneve n fracture an d exposes a medium green-gre y surface. I t is fine-grained , basic , an d contains crea m plagioclase phenocryst s randoml y distrib-uted throughout; feldspa r an d amphibole can be identified i n hand specimen. It s weathered surfac e is rusty-brow n and contain s protrudin g weathered crea m feldspar phenocrysts .

Thin Section : Th e thi n sectio n i s ophiti c an d consist s mainl y of plagioclase, pyroxene , and abundant secondar y chlorite , sericite , epidote , an d sphene . Accessor y minerals ar e quartz and opaque iro n minera l (probabl y magnetite an d ilmenite). Quart z occur s mainl y in the mesostasis , where i t i s commonl y intergrow n wit h alkali-feldspar . Mos t of the plagioclase form s laths, but feldspathic patches , no w extensivel y saussuritized , wer e probabl y also plagioclase phenocrysts . Sericite an d epidot e ar e abundan t in these patches . Grainsiz e averages abou t 1 mm. Sericitiza -tion o f plagioclase make s the determinatio n o f its composition difficult. A few relic t grain s indic -ate a compositio n o f abou t A n

4 5 » T n e Pyroxen e i s a n augite with a moderate positive opti c axial angle . Som e of i t i s altere d to uralitic amphibol e and chlorite.

The dolerit e i s essentiall y autometamorphosed , but may have suffere d sligh t disloc -ation metamorphism . Thi s i s indicate d b y fractures and slight granulatio n o f som e grains ; suc h a condition possibly als o resulte d i n som e uralitization an d sericitization .

DR138: Feldspa r porphyry.

Hand Specimen : Th e roc k i s red-brow n an d igneous , an d is somewha t iron-stained; feldspa r phenocrysts ar e weathere d an d flesh-coloured . A freshl y broken surface show s that quartz and feldspar phenocryst s ar e se t i n a n aphaniti c groundmass ; phenocryst s o f quartz are smalle r than those o f feldspar, which are up to 4 mm. across. Als o in the groundmas s are numerous smal l red spot s (0. 5 mm. diameter), closely spaced , which are impregnatiou s o f groundmas s with finely--divided hematite .

Thin Section: Th e thin section contains plagioclase phenocrysts u p to 2 mm. long in a partly grano-phyric groundmass . Th e re d spots , som e o f which are nearly opaque, can be see n to be brown-stained oligoclas e spherules ; som e o f them are partly silicified . Th e spherules ar e up to 0.5 mm. across. Som e are completel y siliceous , bu t these ar e not iron-stained, an d are readil y identifie d by thei r uniaxia l figure . Th e variou s spherule s ar e abundan t and randomly distributed. Th e groundmass contain s numerou s clea r xenomorphi c quart z grain s an d albit e laths ; som e o f the laths penetrate , o r ar e include d in , the spherules . Lesse r constituent s ar e chlorite , sphene , and opaque iro n mineral ; fleck s o f chlorit e ar e concentrate d aroun d grain margins. Sericit e fleck s the surfac e o f the plagioclase, an d some o f the phenocryst s contai n numerous quartz inclusions a s a resul t o f their silicification .

The roc k i s a feldspa r porphyry , wit h certai n granophyri c affinitie s i n that it s groundmass contain s late-stag e crystallizatio n products , spheruliti c plagioclas e an d quartz , and patche s o f quartz-feldspar intergrowth. However , it has been extensively silicified .

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DR33: Uralitize d and saussuritized gabbr o pegmatite.

The thi n sectio n mainl y consist s o f saussuritize d plagioclase , uralitize d pyroxene , quartz , an d opaque iron mineral. lim e nit e i n the pre-existing iron mineral is altere d to sphene , leavin g grain s with relic t magnetit e blades . Epidot e is an abundant component of the saussurite . Grain s are eve n and averag e abou t 4 mm.

DR38: Granophyri c rhyolite porphyry or granophyric porphyritic rhyolite .

The thi n sectio n i s essentiall y a micrographic intergrowth of quartz and potash feldspar i n which a fe w quart z an d plagioclas e phenocrysts , an d numerous concentrations o f fine-grained chlorite , occur. Th e intergrowt h i s delicat e an d commonl y feathery , an d is cu t by numerous fractures . Opaque iron mineral grains ar e sparsel y distribute d throughout. Th e phenocrysts ar e u p to 1mm. across.

DR49: Quartz-feldspa r porphyry or dacite .

Most phenocryst s ar e plagioclase ; a fe w ar e quart z and opaque iron mineral (som e o f which i s partly converte d t o sphene) . Th e groundmas s i s extremel y fine-graine d an d consists mainl y of alkali feldspa r an d quartz . Accessor y minerals ar e apatite , zircon , an d chlorite; finel y divide d opaque iro n minera l dust s th e thi n sectio n i n places . Mos t phenocrysts ar e 0.5 to 2 mm. long.

DR65: Adamellite .

Grains o f microcline , quartz , sodi c plagioclase,muscovite , apatite , an d opaque iron mineral ar e partly granulated , an d thos e o f plagioclas e ar e sericitize d an d turbid; undulos e extinctio n i s common. Th e muscovit e flake s ar e well-cleaved an d flexed. Grainsiz e is variable ; most grain s are 0. 5 to 4 mm. across.

DR66: Sericitize d quartz-albit e porphyry.

Most phenocryst s ar e microcline ; a few ar e quart z and albite. The y are se t i n a groundmass of quartz, sericite , accessor y biotite , an d rare apatite. Th e rock has been partly granulated. Opaqu e iron minera l grain s ar e wide-spread. Phenocryst s measure up to 1 mm. across, an d quartz grains in the groundmas s average 0. 1 mm.

DR106: Granodiorit e porphyry.

Phenocrysts an d glomeroporphyritic patches o f plagioclase li e i n a partly granophyric crystallin e groundmass. Th e plagioclase i s oligoclase . Mos t of the groundmas s is quart z and alkali-feldspar; small amount s of chlorite , opaqu e iron mineral, and leucoxene, a s well a s accessor y apatite , are present. Partia l granulatio n i s indicate d b y fracture d grain s with undulose extinction an d by numerous crack s ouline d b y iro n stainin g an d mica concentrations. Mos t phenocrysts ar e 0.5 t o 4 mm . long.

DR109: Porphyriti c an d amygdaloidal acid lava .

The thi n sectio n contain s euhedra l phenocryst s o f oligoclase , an d amygdules of quartz and fine mica, i n a finel y granophyri c base. A few aggregate s o f straine d quart z grains hav e opaque iron mineral borderin g th e grains . Som e of the base i s replace d by silica. Smal l spherules (0, 2 mm.

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diameter) occu r throughout ; man y ar e coloure d red-brown . Muscovit e flakes fleck , an d small opaque iro n minera l grain s dust , th e thi n section . Finel y divide d hematite cause s rusty-brow n coloration i n places. Mos t phenocrysts measur e from 1 to 2 mm. and the amygdule s mostly range from 0. 5 to 1 mm. in diameter.

DR110: Quartz-feldspar porphyry or metadacite .

Most phenocryst s ar e o f altere d oligoclase , bu t som e ar e corrode d quartz. Th e groundmass i s feldspathic an d siliceous (partl y silicified i n that silica and sericit e possibl y replac e som e origina l feldspar); som e granophyri c patche s ar e present . Chlorit e and biotite ar e concentrate d int o patches whic h ar e numerou s an d evenl y distributed . Man y of the silicifie d patche s appea r to be spherules o f quartz . Opaqu e iron mineral is scattered throughout ; accessor y mineral s ar e apatit e and sphene . Phenocryst s measur e up to 3 mm., but many are abou t 1 mm. across. Alteratio n i s low-grade regional .

DR123: Rhyolite?

The roc k i s probabl y bes t calle d a rhyolite ; bu t the compositio n o f the feldspa r phenocryst s cannot b e determine d becaus e o f sericitization . Th e other phenocrysts ar e quartz . Th e ground-mass i s extremel y fine-graine d an d consist s o f quartz , alkali-feldspar , an d sericite. Smal l grains o f opaqu e iron mineral occur throughout . Zirco n i s accessory . Phenocryst s measur e up to 1 mm . across .

DR125: Dacite .

Phenocrysts ar e plagioclase an d corroded quartz; criss-cros s patche s o f biotite probabl y replace original ferromagnesia n minerals . Mos t phenocrysts ar e oligoclase . Mino r minera l constituent s are calcite , chlorite , sericite , apatite , zircon , sphene , an d opaque iron mineral . Th e groundmass is ver y fine-grained , crystalline , an d fairl y siliceous ; i t contain s quartz , alkali-feldspar, and numerous smal l sericit e flakes . A poor flow-structure is discernible , especiall y aroun d the many euhedral plagioclase phenocrysts . Phenocryst s measure up to 3 mm. across. Th e rock has under -gone low-grade metamorphism.

DR129: Spheruliti c granit e porphyry.

Nearly al l th e phenocrysts ar e albite ; th e remainder are quartz , and are muc h smaller than those of plagioclase . Th e groundmas s contains numerou s spherule s o f orthoclase , subordinat e quartz, and mino r quantitie s o f albite . Opaqu e iron mineral grain s ar e fairly numerous , and iron-stain -ing i s no t uncommon . Accessor y minerals ar e leucoxene , chlorite , sphene , an d apatite. Plagio -clase phenocryst s measur e u p t o 1 mm., whereas th e quartz phenocrysts ar e only about half this size.

DR139: Apliti c granite .

The thi n sectio n consist s o f xenomorphi c microcline , quartz, and sodic plagioclas e grains . Th e plagioclase i s partl y altere d t o sericit e an d clay , wherea s th e microcline i s absolutel y fresh . Both muscovite an d biotite ar e present; som e of the biotite i s altere d to chlorite ; accessor y min -erals ar e zircon , apatite , sphene , an d opaque ironmineral. Secondar y minerals ar e calcite , epid -ote, sericite , an d chlorite . Th e textur e i s granula r or saccharoidal ; grainsiz e average s abou t 0.2 mm. ; som e grain s measur e up to 0.5 mm.

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DR141: Fine-graine d basi c igneou s roc k - probabl y metabasalt.

30

Small feather y needle s o f actinolit e amphibol e li e i n a reconstituted feldspathi c groundmass ; (andesine, abou t A n ) opaqu e iro n mineral grains ar e evenly distribute d throughout . Accessor y minerals ar e chlorite , sphene , biotite , an d apatite . Th e rock is fine-grained , an d averages 0. 2 mm.

PLATE 1

REGIONAL GEOLOGICA L MAP

THE DAVENPOR T AN D MURCHISO N RANGE S

NORTHERN TERRITOR Y

4 Mile s t o 1 Inc h (APPROXIMATE)

Geology an d comp i l a t i o n b y : K . G . Sm i th , J . R . Stewart , J . W . Smi t h

Drawn b y : W . G . Kraus e

o N

o < o

o o M

o UJ

< < 0 _

MIDDLE CAMBRIAN

UPPER " PROTEROZOIC?

Sandover Bed s

Gum Ridg e Format ion

< on CD

< O UJ cc CL

LOWER PROTEROZOIC?

Hatches

Creek

Group

War ramunga Group

Bureau o f M i n e r a l Resources , Geolog y an d Geophys i cs ,

Reference 940'

951'

Qa or.

I z 7

6

A / f a u i u m , soi/ , s a

Soft u;hi( e amorphous limestone with some flint nodules

Shale, sandstone, chert, limestone

Shale, sandstone, chert, limestore

Uncon fo rm i t y

Banded medium-grained, ripple-marked, cross-bedded

quartz-sandstone and boulder conglomerate

Uncon fo rm i t y

F + H- + -H

Two-mica microcline granite

Quartz-feldspar porphyry

Acid and intermediate intrusives

II>v lit Basic intrusive gabbros and differentiates

/AVAVAVAX , , , rAVAVAVAV; Basic flow : AVAVAVAVA

Thin-bedded, cross-bedded, ribble-marked medium and coarse-grained sandstone and silicified sandstone ; pebble conglomerate, greywacke, shale, siltstone

Acid and intermediate type extrusive rocks

Uncon fo rm ity

Greywacke, sandstone, chert, jasper, siltstone, shale

Area mappe d an d index t o adjoining sheet s

Tennant Creek

Alroy Ranken

Bonney Wel l $ Frew Rive r Avon Down s

Barrow X Creek

^ Elkedr a Sandover River

Frew Rive r • con t ro l l ed Bonne y W e l l ,

Bar row Creek , Elkedr a • u n c o n t r o l l e d

M a p p i n g : Reconna issanc e o n a 4 -mile scal e