| Abstract |
The Tongonan hydrothermal fluids are up to 2 orders of magnitude undersaturated with respect to the base-metals which appear to have precipitated in the reservoir rocks as sulphides. These fluids currently deposit a significant amount total Pb, Zn) of base-metals within an amorphous silica bas ein artificial drains and channels. A variety of opaque minerals occur in these scales, vis : base-metal eulphides, pyrite, marcasite, silver sulphide, sulphosalt, electrum, dignite- chalcocite, fahlore, pyrrhotite, bornite, hematite and goethite. Their textures closely compare with advanced breccia bodies; such textures are apparently preserved i n nature as they are observed in some hydrothermal ore deposits. Two important implications of this study are: a ) Research on mineral deposition is highly relevant to the environmental and utilisation problems associated with the discharge of geothermal effluents, particularly the high arsenic and lead that are dumped into and pollute waters and blockage of production and reinjection wells and surface equipment by silica; b) The precipitates containing variable amounts of metals represent the last phase deposited by the most recent geothermal water reequilibration attempt in the wells; the high metal content of these materials demonstrate the ability of the metal and sulphur deficient Tongonan geothermal fluids to transport and deposit metals. |