Bulletin of the Geological Society of Malaysia, Volume 19, April 1986, pp. 293 – 302
Department of Geology, Gauhati University, Guwahati-781 014, Assam, India
Abstract: A probable plate-junction and ophiolite belt which run from Western China, roughly in a southern direction and extending up to the Andaman-Nicobar Islands in the Indian Ocean, is one of the least geologically known structures in the world.
Nearly all the rivers and streams flowing in this vast territory are known to carry minute amounts of placer gold. Our investigation of the source of this gold, in a very limited area of Eastern Manipur showed that primary gold mineralization took place in two phases-magmatic and hydrothermal. On the basis of the paragenetic mineral association, the magmatic phase can be further divided into two sub-phases-oxide phase, where the associated minerals are chromite and magnetite and the sulphide phase, where the associated minerals are pyrite, pyrrhotite and Co-Ni-Cu sulphides. In the oxide phase, gold occurs as minute blebs and flakes of gold-copper amalgam, sometimes as inclusions within chromite crystals and magnetite veins. In the sulphide phase, the presence of gold can be ascertained by chemical and other methods but visible gold particles are rare.
In the hydrothermal phase, gold occurs as auricupride within the serpentine veins, where the primary associated minerals are Iimonite-geothite; but the major source of gold is the high temperature quartz veins cross-cutting the ultrabasics and surrounding sedimentary rocks.
Some of the “granitic” rocks with which gold mineralization was formerly associated were found to be highly metamorphosed graywackes enveloped by ultrabasic rocks.