Metalliferous Sediment Deposits Classroom

METALLIFEROUS SEDIMENT DEPOSITS

A sediment core from the Red Sea shows red and brown layers of sediments rich in copper, iron, zinc, and other metals. These sediments provided some of the first evidence that metal-rich minerals could be found along mid-ocean ridges. (Photo courtesy of David A. Ross, WHOI)

WHAT ARE METALLIFEROUS SEDIMENTS?

HOW AND WHERE DO THEY FORM?

RED SEA METALLIFEROUS SEDIMENT DEPOSITS

SAUDI-SUDANESE RED SEA JOINT COMMISSION AND MINING OPERATIONS

BENEFICIATION

DISPOSAL OF TAILINGS

BAUER DEEP METALLIFEROUS SEDIMENTS DEPOSITS

WHAT ARE METALLIFEROUS SEDIMENTS?

Sediments with anomalously

High Fe, Mn, Zn, Cu, Ag, U, Si/Al, but

Low Ti, Cr, Sc, Al and Th when compared to normal pelagic clays.

Fe/Mn = 1 to 200

HOW AND WHERE DO THEY FORM?

Hydrothermal activity• Precipitates settle on the ocean floor – to form

metalliferous sediments• Sometimes transported by currents and deposited in

deeps/ depressions. Example: the Bauer Deep in the Pacific.

OCCURRENCES

• Atlantis - II Deep (Red Sea)

• Tonga-Kermadec Ridge

• North Fiji Basin, east of Australia

• Woodlark Basin

• Bismarck Sea

• Between the Clarion and Clipperton Fracture Zones

• Back-arc basins and volcanic arcs

• ''Basal'' metalliferous sediments – Geochemical evidence for seafloor spreading.

From 1968 to 1983, the Deep Sea Drilling Project collected sediment cores from around the world using the drilling vessel Glomar Challenger, a 400-feet long ship designed to drill in deepwater. Many of the cores contained metal-rich sediments on top of the volcanic rocks of the ocean crust. (Photo courtesy of the Ocean Drilling Program)

ANCIENT ANALOGUES

• The Devonian Rammelsberg and Meggen Ores of Germany

• The Lower Carboniferous Tynagh of Ireland

• The Precambrian Mt. Isa deposits (1.6 Ga old) of Australia

• The Cretaceous copper deposits of Cyprus

• All lead - zinc ores.

• Rea Sea – An ''infant'‘ ocean

The Red Sea is a juvenile ocean basin that is forming as the African plate diverges from the Arabian plate.

New basaltic ocean crust is just beginning to form in the center of the Red Sea.

RED SEA METALLIFEROUS SEDIMENT DEPOSITS

• Rift system tectonically active, producing several deeps (depressions)

• Only the Atlantis - II Deep has economically viable deposits

• 1948 - First indications of high heat flow, high salinity

• 1963 - Metal-enriched sediments collected

Dr. David A. Ross of Woods Hole Oceanographic Institution examines a sediment core collected in the Red Sea during a 1965 expedition on board R/V Chain. (Photo courtesy of WHOI Archives)

Dr. Andre Antunes' (KAUST RSSE) 5um pre-filter coated in metalic minerals after filtering liters of Atlantic II brine water.

• Detailed survey by R.V. Atlantis

• 1967 - First appraisal of the economic significance of the deposits

Atlantis – II Deep metalliferous sediment deposits

• Average thickness 10 m (sometimes up to 30 m thick)• Average water depth 2,180 m (range 2,100-2,200 m)• Areal extent 60 sq. km.• Light in color but dark chocolate brown near basement• Consistency: like shoe polish• Variegated and laminated• Limonitic and haematitic facies (under oxidising conditions)• Sulphidic facies (under reducing conditions)• Estimated reserves:- 100 million tons (m.T) of dry, salt-free

material with 2.5 m.T Zn, 0.5 m.T Cu, 9,000 T Ag and other metals.

SAUDI-SUDANESE RED SEA JOINT COMMISSION AND

MINING OPERATIONS

• Saudi Arabia and Sudan have: Exclusive rights up to 1,000 m water depth Exclusive and equal rights beyond 1,000 m

water depth• Red Sea Joint Commission for mining the

Atlantis-II deposits

MINING EQUIPMENT

• Vibrating suction head with water jets- to loosen the sediment and convert it into slurry

• Heavy duty pumps- to pump up the slurry

• Pipeline from the sea bottom to the ship-to transport the slurry from sea bottom to the ship.

•Suction in 1 m-steps, up to 18m depth or to the hard anhydrite layer.

BENEFICIATION

Options:• Shore-based processing (large no. of tankers)• Setting of particles (mostly < 2 m diameter)• Centrifugation (not viable)• Froth flotation (proven technology)• 2000 T of mud through a series of 12 floatation

cells yield: 4 tons of dry, salt-free concentrate with 25-40 % Zn ,Cu and Ag

• 99.8% of the slurry is tailings!

DISPOSAL OF TAILINGS

• Pre-pilot mining test• 90-95 % of the original input disposed off at

400m depth through a 6” diameter pipe.• Tailings plume monitored; drifting and settling

behaviour of particles investigated.• Claim: Tailings settle to 1,200 m in a short time.

No appreciable impact on marine life.• Another opinion: Disposal should be at > 800 m.• Conflict between development and environmental

protection.

BAUER DEEP METALLIFEROUS SEDIMENT DEPOSITS

• Far away from the EPR, in the sub-equatorial Pacific

• Metalliferous sediments under 4,000 m of water.

• 18 % Fe, 6.5 % Mn, high concentrations of Cu, Ni and Zn.

• Lower metal contents, but greater thickness and areal coverage.

Average Pacific Sediments

Bauer Basin Sediments

North manganese

Equatorial Nodules

Mn 11,000 51,000 710Fe 58,000 175,000 180Cu 660 960 29Ni 290 500 43Co 140 200 5**Mo 41 310 1**Zn --- 720 3**Pb 135 170 1**V 400 170 1Ag --- 2 --

*Values in millions of metric tons estimated for Bauer basin area below 4,000-m contour, 3.1 X 105 km2 For Bauer basin and average Pacific sediments, the same depth of sediment (10m) and dry bulk density (0.3 g/cc), were used. Chemical compositions from Table 1. For northern equatorial manganese nodules, a nodule coverage of 9 kg/m2 and dry density of 1.4 g/cc were used (Mero, 1977). Chemical compositions from Dugolinsky (1976). ** from Cronan and Tooms (1969).

Table 2. Resource Comparisons for Bauer Basin Sediments, Average Pacific Sediments and Northern Equatorail Manganese Nodules