Mining in Manitoba

OCEAN MINING

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There are about 140 sites of presently or recently active hydrothermal venting on the sea floor and more are being found every year by marine geologists, geophysicists and biologists conducting basic research on a fundamental Earth process. This is one important way that heat is ventilated from the interior. The vented hot water, at temperatures as high as 420C but more commonly 350C, carries dissolved in it high concentrations of metals, reduced sulfur and other elements that are precipitated when it encounters the 2C bottom water. The mineralogy and fundamental geology of the larger deposits would be familiar to anyone who works with volcanogenic massive sulfides (vms) on land.

Most of the 140 or so known sites are just geochemical anomalies -- metalliferous sediments, vents with little or no mineralization, thin crusts, small chimneys and mounds that would fit comfortably inside a small house. Some, however, are large, such as the main active mound at the Trans-Atlantic Geotraverse (TAG) site on the mid-Atlantic Ridge east of Miami or the Magic Mountain site on Explorer Ridge about 200 km west of Vancouver Island. These are comparable in size and shape to Toronto's Skydome, a covered baseball and football stadium, which makes them to be in the 3 - 5 million metric ton (mmt) range and there are several more large mounds at both sites. This size is comparable to the typical 1 - 3 million metric ton vms found today on land in Canada but, of course, nothing at all like the giant Brunswick #12 deposit (134.1 mmt) in New Brunswick or Kidd Creek deposit (117.5 mmt) in Ontario.

The largest of all the ocean vms deposits, the Atlantis II Deep in the Red Sea, is 94 million metric tons. These metal-rich muds were carefully assessed by the German company Preussag on behalf of the Sudanese and Saudi Arabian governments in the 1970s. At 0.45% copper, 2.07% zinc, 39 grams/ton silver and 0.5 grams/ton gold, but with higher grade sections, the deposit was considered to be uneconomic. Regardless, that is a similar grade to the average for the 85 deposits totaling 1765 million metric tons comprising the Iberian Pyrite Belt in Spain and Portugal (0.8% Cu, 2.0% Zn, 0.7% Pb, 26 g/t Ag, 0.5 g/t Au).

Next in size appear to be the mounds at the Middle Valley site off the west coast of Canada totaling about 25 million metric tons. These mounds are growing in thick sediments and have some attributes to deposits on land. Recent drilling by the Ocean Drilling Program, of which Canada is a member  has shown that one of mounds contains 220 metres of stacked sulfide lenses and intervening feeders from which 8 representative samples gave average values of 3.3% Cu, 19.6% Zn and 0.1% Pb. Beneath is a "Deep Copper Zone" that is about 40 metres thick and is returning copper assays of >10%. A wonderous build-up of metals is happening now off Canada's west coast. Scientists from the Scotiabank Marine Geology Reserch Laboratory at the University of Toronto have found several mounds of metal sulphides within Canada's 200 nautical mile economic zone and in the southwest Pacific near Papua New Guinea. The lab continues to work on the mystery behind the formation of these large deposits. .

The true grade, in a mining sense, for any of deposits, except for the Atlantis II Deep, is not known. Most of the sampling has been by submersible and dredge which typically scrapes the exterior of a mound or takes part of a chimney. These tend to be quite spectacular. Fifty-nine analyses from TAG, for example, averaged 6.3% Cu, 25.2% Zn, 0.04% Pb, 378 Parts per million (ppm) Ag, 5.7 ppm Au. However, ODP drilling into TAG found that the interior was mostly relatively barren pyrite and anhydrite. Analyses of the ODP core average 2.2% Cu, 0.6% Zn, 0.0% Pb, 9 ppm Ag, 0.5 ppm Au. These discouraging results, from a potential economic point of view, do not seem to have been repeated at Middle Valley, though. It is probable that, just as is the case for land deposits, some seafloor vms, like TAG, will be teasers with some high grade parts but mostly low grade while others will be spectacular.

The eastern Manus Basin (EMB) is an approximately 4000 km2 pull-apart basin between two transform faults in arc crust of New Britain and New Ireland. Felsic volcanic ridges, mostly dacite and rhyodacite, are surrounded by andesite and basalt, very reminiscent of the famous Noranda vms district of Archean age.

Basic field work at EMB has consisted of detecting hydrothermal particulate plumes using an instrument package that was "tow-yoed" between 20 and 300 metres off bottom behind a ship, deep-tow camera-video traverses and sampling by dredge and sediment corer. A joint Japanese-French submersible expedition in 1995 on which Roger Moss and Ray Binns participated conducted detailed mapping and sampling. Extensive zones of hydrothermally active and dead chimneys, massive sulfides and altered hyaloclastite were discovered on two large ridges (PACMANUS and SuSu Knolls). The massive sulfides at PACMANUS, predominantly chimneys without underlying mounds, lie on the flanks of effusive felsic volcanic domes at a water depth near 1700 metres. Initial analyses of 26 random samples averaged 10.9% Cu, 26.9% Zn, 1.7% Pb, 230 ppm Ag and 15 ppm Au.

The SuSu site is even better. Here, there is about 5 km strike length of hydrothermal products and active venting. The main massive sulfide lens (called Suzette) is at a water depth around 1600 metres. It appears to be about 1200 metres long and 200 - 300 metres wide but of unknown thickness. Binns' average of 24 analyses of 15% Cu, 2% Zn, 130 ppm Ag and 21 ppm Au is rather spectacular. That these deposits are so very gold rich should not be surprising when it is considered that EMB lies within a gold metallogenic province that stretches some 25,000 km from Kyushu, Japan (e.g., Hishikari gold mine) to the Taupo Zone of North Island, New Zealand. The very gold-rich Lihir Island deposit is just a stone's throw to the east of EMB on the other side of New Ireland.

Conceptual Mineral Recovery System
Conceptual Mineral Recovery System
It is these spectacular analyses and potentially large tonnage that attracted Nautilus Minerals to the EMB area. They now hold an exclusive exploration license from the Papua New Guinea government. Will they be able to do the first seafloor mining of a vms here? Maybe. Nautilus is dealing with permitting from a single friendly government, instead of the UN if the site had been in international waters and, being in the ocean, there will be no competing land claims from special interest groups as commonly happens on land. The environmental consequences of ocean mining may be less deleterious than land mining. There will be no acid mine waters to contend with because sea water, being alkaline, would neutralize any acids that may form and submarine weathering is a very slow process in any case. There will be no gaping holes on the sea bed and no huge rock piles; the deposits are sitting on the sea floor uncovered. Besides, it would be technically difficult and very expensive to excavate in lavas compared with extracting rather crumbly, poorly consolidated polymetallic sulfides. Some fauna are bound to be killed but a competent biological assessment prior to mining can determine whether or not this would lead to species extinction.

The technology for extracting bulk samples from the sea floor does not yet exist in total but some engineering can be borrowed from the ill fated manganese nodule programs of the 1970s. The Japanese are developing an ocean miner which is said could be used both for manganese nodules and polymetallic sulfides. Actually, polymetallic sulfide recovery from the rather shallow seabed at EMB should be easier than for manganese nodules where depths are on the order of 5500 metres. The Japanese may be in a position to try out their new miner on a vms deposit of their own. Their Metal Mining Agency has recently announced that they have begun a 5 year feasibility study of a large deposit they have found in the Okinawa Trough at about 1600 metres water depth between Taiwan and Kyushu.


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