Here is more on Kambalda deposits that is clear.
en.wikipedia.org
Here is something related on a similar type, Besshi deposits, of which an instance was the late lamented Windy Craggy in B.C.
Economic Viability
Besshi-type volcanogenic massive sulphide (VMS) deposits range in size from under a million to 300 million tonnes and grade between 0.64% and 3.3% copper. The Besshi deposits themselves contain 30 million tonnes of 2.5% copper and 0.3% zinc, plus 7 grams silver and 0.2 gram gold per tonne.
Examples of Besshi deposits in Canada include Windy Craggy, in northwestern British Columbia, which is said to contain between 210 and 320 million tonnes of ore grading 1.66% copper, 0.09% cobalt, 3.5 grams silver and 0.2 gram gold, and Soucy, in the northern Quebec's Labrador Trough, which contains 4.3 million tonnes of 1.4% copper, 1.09% zinc, 19 grams silver and 2 grams gold.
Windy Craggy is by far the world's largest known Besshi-style deposit. Some authors suggest that the Britannia mine in southern British Columbia, which contained 48 million tonnes grading 1.9% copper, 0.65% zinc, 6.86 grams silver and 0.69 gram gold, might also be a Besshi deposit.
In the Proterozoic continental margin of the Appalachian Orogenic belt of the U.S., the Ducktown massive sulphide in Tennessee contained 163 million tonnes with an estimated 1% copper and 0.9% zinc, whereas the Gossan Lead deposits in Virginia had 20 million tonnes of 0.5% copper and 1.5% zinc.
Besshi deposits occur in Proterozoic to Mesozoic rocks, while the age of most deposits is late Proterozoic to early Paleozoic (1.4 billion to 400 million years). It has been suggested that modern-day sediment-covered examples of Besshi mineralization are forming in the Guaymas Basin in the Gulf of Mexico, the Middle Valley of the Juan de Fuca Ridge (off Vancouver Island) and the Red Sea.
These deposits have low base metal grades and consequently high sulphur contents. Many deposits -- Gossan Lead, for example -- were actually mined for their sulphur and not for their base metals. The high sulphur contents can present environmental problems for the mining and refining of ore.
The deposits appear to have formed in a variety of tectonic environments, from oceanic crust to early-forming rift basins in continental plates. The host rocks are thick, terrigenous clastic sedimentary sequences with lesser tholeiitic mafic magmatism. It has been suggested that the size of the deposit reflects the volume of mafic volcanic rocks in the ore-forming system; the more mafic volcanic rocks present in the basinal stratigraphy, the more copper there may be in the exhalative sulphide body. The deposits would have relative copper, zinc, silver and cobalt enrichments that could be delineated by regional lake and stream-sediment geochemical surveys.
Geochemical definition of tholeiitic basaltic magmatism in a thick sequence of clastic sedimentary rocks, or their metamorphosed equivalents, would be a useful method of regional exploration. It is a reflection of their deformational states that Besshi deposits, unlike other VMS deposit-types, do not commonly exhibit extensive feeder alteration systems in the footwall to the massive sulphide bodies. Alteration is usually a broad enveloping chloritic halo, which may be reflected by a relative magnesium enrichment in country rock. Lithogeochemical surveys of cobalt versus nickel distributions might also be useful, given that the Besshi sulphides have a distinctive cobalt-nickel ratio greater than one.
Although the deposits are composed of metallic sulphides, the abundant graphite in the sedimentary rocks (or their metamorphic equivalents) around these deposits would make it difficult to carry out airborne electromagnetic and magnetic surveys. Ground geophysical surveys using induced polarization and electromagnetics may aid in the delineation of the massive sulphide horizons.
-- The author is a professor of geology at Memorial University in St. John's, Nfld.
Here is some stuff I wrote when I could write a lot better.. I guess I was inspired..
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