层、相、位对广西北山银、锌、镉、黄铁矿矿床的控制作用探讨

一、概述本矿床是一个以银、锌、镉、黄铁矿为大型,铅为中型的硫化物矿床。它兼有我国南方泥盆系碳酸盐岩层控铅—锌矿床和层控黄铁矿矿床的主要地质特征,是一个研究典型层控矿床和成矿理论不可多得的矿床,因此不少专家学者前往参观考察。矿床位于扬子准地台东南缘,在南华后加里东准地台上,处于“江南古陆”南端西南缘,桂中褶断束的北西段,于南岭多金属成矿带西端,属北山—泗顶铅、锌、黄铁矿成矿远景区的西段。矿床周围出露大片泥盆系和石炭系,它的北部和东部是江南古陆,出露有四堡群、板溪群、震旦系及零星分布的寒武系,西北角和南西偶有二叠系出露。

An Approach to the Controls of strata,Sedimentary Facies and Location on the Beishan Silver,Zinc,Cadmium and pyrite Deposit in Guangxi

The Beishan deposit in Guangxi, a large-scale sulfide ore deposit in which silver, zinc, cadmium and pyrite occupy first place : lead comes second, is situated on the outer side of the southwestern margin at the southern end of the Jiangnan old land, i. e., at the northwestern end of the central Guangxi folded fault boundle. The Devonian and Carboniferous strata cropped out around the deposit, and the pre-Devonian strata and the magmatic rocks of various types on the old land to the north and east of it. The development of the study area involved both Pre-Caledonian geosynclinal and post-Caledonian paraplatformal stages. The geosynclinal history in the area ended as a result of Caledonian Movement during which the NNE-dominated and NWW-subordinated tectonic framework was formed. The combination of the ancient NNE-trending fault zones led to the formation of many finger uplifts on the margins of the old land Which stretch southwards into the marine basin and constituted a series of finger bays with rises alternating with depressions. During early and middle Early Devonian, the area was once a denudation area and then received the littoral elastic deposits due to transgression in the late stage, while from Middle to Late Devonian, although a larger-scale transgression resulted in the development of organic reef facies in some parts of the uplifted area, the area was still dominated by shallow-marine carbonate rocks. Since the areca was adjacent to the margins of the old land, many rivers on the old land poured into the marine basin and provided abundant mineral material for the area. In addition, the migration and accumulation of the mineral material gradually from the depression to the uplifted area contributed to the formation of the deposits in the area under the influence of folding, faulting, organic reefs, dolomitization and other geological processes. There are well-developed strata, from old to new, cropping out in the Guangxi area, among which the Devonian strata act as the most important ore-bearing horizons. For example, the Devonian Pb-Zn deposits occupy first place in the area both in the numbers of mineral occurrences and in the reserves. The controls of sedimentary facies and palaeogeographic environments on the ore deposits (orebodies) are included as follows. (1) The NNE-trending zonal distribution of the deposits (mineral occurrences) is controlled by the uplifted areas on the margins of the old land; (2)the distance of the deposits (mineral occurrences) from the margins of the old land vary with different rises and depressions; (3) the deposits (orebodies) are all confined to the transgressive cycles at some distance above unconformity interface; (4)the enrichment of the deposits (orebodies) is governed by lithologic associations, source beds, reservoirs and overlying strata, and (5)the emplacement of the deposits (orebodies)by the anticlines and the faults on the anticlines in the uplifted area at the Devonian sedimentary basement.