Abstract

Report of the 11th AGM of the Mineral Deposits Studies Group held in the Department of Applied Geology, University of Strathclyde, Scotland, 19–21 December 1985.

The meeting titled 'Genesis of, and exploration for, industrial and ore minerals' was attended by 92 participants (from academia and industry) and included a field trip, 38 papers and several poster sessions. On the first day M. J. Russell and A. J. Hall led a field trip to Tyndrum where dumps, veins and wall rocks were examined in drizzle.

A keynote address on Black Smokers and a video taken by submersible were given by John Edmond. He described hydrothermal activity on intermediate and fast spreading ridges in the Eastern Pacific. The fluids are of sea-water origin, acid (pH about 3) and with temperatures around 350 °C. Chloride is the only anion and H2S concentrations reach 300 ppm whereas Cu and Zn are usually between 1 and 5 ppm. While the metalliferous sediments are analogues to ophiolite-type massive sulphide ore bodies no active example has been found that remotely compares to them in size. Most of the ore-forming metals are lost as 'black smoke' and the ore localization mechanism is a puzzle.

Hydrothermal fluids from the Gulf of California are alkaline, contain major ammonium and are depleted in ore metals possibly suggesting that a sediment-hosted massive sulphide deposit is forming at depths. Precipitation may be caused by reaction of the ore fluids with biogenic carbonate tests and with ammonia produced by the thermocatalytic breakdown of

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