桂西北地区岩浆活动与超微粒型金矿化的关系

在简要介绍桂西北地区岩浆活动特征和论述超微粒型金矿床成矿期次、成矿物质及流体来源、热源的基础上,探讨了岩浆活动与超微粒型金矿化的关系.本地区大地构造演化、尤其是岩浆活动与金成矿过程具有明显的对应关系:华力西-印支期准地台-再生地糟发展阶段的海底基性岩浆侵入和喷溢活动,对应形成矿源层的沉积成岩初步富集期,即由于海水浸蚀使岩浆物质中的金解离,往海水搬运、生物作用,在隆起区边缘沉积环境变换带沉淀聚集形成相对富集的转生矿源层;印支晚期-燕山期大陆边缘活动带发展阶段酸性岩浆活动对应热液主成矿期,即酸性岩浆活动不仅提供了成矿热液的热源,而且岩浆热液参与了成矿并提供了部分成矿物质和成矿流体.

RELATIONSHIP BETWEEN ULTRAMICRO-GRAINEDGOLD MINERALIZATION AND MAGMATISM IN NORTHWEST GUANGXI PROVINCE, CHINA

Northwest Guangxi underwent a crustal extension-depression environment during Variscan-Indosinianepoches, when magmatic activities took place frequently and intensely, and multiphase basic volcanic rockswere formed broadly. In Yanshanian epoch, the area was situated in a continental marginal mobile belt, wherehiden granitoid was developed, but only a few small acid rock bodies and dykes outcropped.The ult ralmicro-grained gold deposits in Northwest Guangxi experienced depositional-diagenetic primaryenrichment stage, main hydrothermal mineralization stage, and supergene oxidation-leaching and enrichmentstage. The ore-forming materials were derived from late paleozoic carbonate formation in the upwelling areawithin depression region, from outer Triassic sandy mudstone, and partly from magmatic hydrothermal. Studyon H and O istope-tracer and mineral inclusion composition suggests that the ore-forming fluid be mainly from infiltrated mereoric water, and secondly from magmatic water. The heat sources are geothem, concealedmagmatic activities and structural stress heat.The tectonic evolution, especially magmatic activities, of the area shows an obvious correlation to themineralization of ultramicro-grained gold deposits. The submarine basic magmatic intrusion and eruption duringVariscan-Indosinian period is corresponding to the depositional-diagenetic primary enrichment stage, in whichthe source bed formed. That means, by etching and transporting of sea-water, the Au from basic magmaprecipitates and concentrates in the sedimental environment transformation belt on the margin of upwellingarea, forming relatively enriched derivative source bed. The acid magmatic activities developed in continentalmarginal mobile belt during late Indosinian-Yanshanian epoches corresponds to the main hydrothermalmineralization stage. The multiphase inherited reactivation of basement faluts at the margin of upwelling arearesults in upwelling and mineralizing of ore fluid. The acid magmatic activities not only contribute to part heatsource for the ore fluid, but the magmatic hydrothermal may also be involed in mineralization by supplying apart of ore-forming material and fluid.