The Role of Organic and Carbonaceous Matter in the Formation of Cariin-type Disseminated Gold Depos-its

摘要

A number of Carlin—type disseminated gold deposits occur in the Au—Hg—Tl-As—Sb mineralized belt of Guizhou-Yunnan—Guangxi triangular area, SW China. On the basis of geology and experiments, this paper discussed the influence of organic and carbonaceous matter upon gold migration and deposition in these gold deposits. The Upper Permian coal measure strata in this area were rich in biogenic organic matter, which might combine with such metallogenic elements as Au, Hg, Tl, As and Sb to form various types of complex organometallic compounds, thus resulting in pre-enrichment of these elements in the Upper Permian strata of this area. Owing to high volatility the organogold compounds would mi-grate upward in the form of gaseous phase organogold compounds under the condition of regional thermometamorphism, collect in anticlines and domes of Upper Permian to Middle Triassic strata, and usually preferentially permeate among porous rocks dominated by siltstone. Physical—chemical conditions changed abruptly during the fault movement which took place along dynamometamorphic zone, causing the decomposition of gaseous phase organogold compounds. Accompanied by the cracking of organic ligand into dispersive car-bon, gold, together with arsenic, entered the lattice of arsenopyrite and arsenic—bearing pyrite. Gold is mainly hosted by sulfl.de minerals in invisible negative charge state, with a small amount adsorbed by carbonaceous materials. This was the principal metallogenic epoch of gold deposits that formed fine-disseminated carboniferous primary ores in the area. The disintegration product of organic materials, such as organic acid, HjS, CO and CO2, set off strong superimposed hydrothermal process after the principal metallogenic epoch. Silicification and carbonatization, associated with cinnabaritization, antimonitization and realgaritization, were superimposed upon fine-disseminated auriferous sulfide mineralization. Limonitization and clayization in supergene leaching—oxidation often further reformed the primary ores and formed oxidized ores in which gold mainly occur as free and adsorbed native gold particles. This type of ore is easy to be dressed.