Evolutionary paleoecology

Paleozoic and Mesozoic-Cenozoic granitoids of the Chilean Andes were studied magnetically in the area between Latitude 22-35•KS. The Paleozoic granitoids are found to be composed of the ilmenite-series and oxidation status of the granitic magmatism.

Feasibility studies on the Okuaizu geothermal field have been carried out to test the possibility of generating 65,000kW of electricity. A production well, 87N-15T,drilled to a depth shows the highest productivity in the geothermal field. It produces geothermal fluid of high temperature (300•Ž at the well bottom ) and high salinity (Cl-: 15,300•`18,500 mg/ •¬). A heavy metal precipitate containing high amounts of gold and silver(max: Au=116ppm, Ag=3.49%) was discovered inside the two=phase (vapor and water) pipeline in front of the separator where pressure and temperature drop from 60kgf/cm2 and 275•Ž to 8.4kgf/cm2 and 171•Ž. The texture and mineralogy of the precipitates were examined as were the chemical properties of the fluid to the surface from the underground reservoir. The precipitates deposited in the pipe before the separator are dominated by sulfides, mainly tetrahedrite with subordinate amounts of sphalerite and galena. These minerals are minute in size and occur in inter...

Three lines of evidence which support the magmatic hydrothermal origin of kuroko deposits are evaluated. (1) Mineralization of kuroko deposits took place around 15 Ma, at the same time as several other geologic episodes including a major shift in the tectonic stress field, a peak of bimodal volcanic activity, and a maximum degree of subsidence. The style of eruption of rhyolite changed from lava flows, acid hyaloclastites, and lithic tuff breccias before mineralization to extensive post-ore pumiceous pyroclastic flows. In an analogy with the Yellowstone caldera, absence of pre-ore basalt directly below the known kuroko deposits suggests that contemporaneous acidic magma existed at a depth of a few kilometers with the potential to release magmatic fluid. Basalt lava is often seen in the hanging-wall sequence of kuroko deposits; it extruded after the acidic pluton had solidified subsequent to mineralization. The post-ore pumiceous pyroclastics could have been produced by violent subma...