Studies on mineralization and composition of DC ore field,Guangxi, China

DC, a multi-metal ore field, is an important and well known producer of tin in China. Besides tin, also mined are zinc, lead, antimony, copper, arsenic, tungsten, mercury, silver and many other metals. Most of the deposits in this region occur in Devonian limestones and siliceous shales. The ore deposits in this field are predominated by cassiterite sulphide type. As to the origin of those deposits, they seem closely related to biotite granite. The ore-forming material is mainly derived from magmatic rocks, and part of it may come from the host rocks. The appearance of horizontal zoning of ore deposits in this field is extremely distinct, with LXG biotite granite as the core. Found in the magmatic rocks is molybdenum mineralization. From the biotite granite outwards there displays such an occurring sequence as the following: copper (zinc) skarn ore deposits, scheelite ore deposits, wolframite ore deposits, cassiterite sulphide ore deposits, lead-zinc (antimony) ore deposits and mercury or arsenic ore deposits. In this region the mineralizing-temperature zoning is also distinguishable, basically in agreement with the horizontal zoning of ore deposits. In other words, the formation temperature of ore deposits occurring around the granite is higher than that farther away from the granite. The following mineralization periods and stages can be divided: the first period, including skarn sub-stage, cassiterite-quartz sub-stage, cassiterite-sulphide sub-stage, cassiterite-calcite sub-stage; the second period, including ferrosphalerite (galena)-franckeite sub-stage, jamesonite-boulangerite sub-stage; and the third period, including pyrite-calcite sub-stage. The characters of material composition are as follows: ore minerals are characterized by great variety, perfect crystallinity, large grain-size and abundant sulfosalts. More than 90 species of minerals have been identified. What is more interesting is that lead and antimony in some of the cassiterite-sulfide deposits are derived from jamesonite rather than galena and stibnite, which provides an example rarely encountered in metallic deposits throughout the world.