广西大厂层控锡石—硫化物多金属矿床的地质特征及形成机制探讨

作者们经过几年来对大厂锡石—硫化物多金属矿床的详细观察和系统研究表明,大厂锡石—硫化物多金属矿床具有明显的层控特征:(1)主要矿体受中上泥盆统地层控制,并呈层状,可以与地层同步挠曲;(2)矿体内保留有典型的沉积成因的结构构造;(3)层状矿中黄铁矿内的Co/Ni比值小于1;(4)矿区及邻区的含矿层位内发现有火山物质存在。主要来自燕山晚期花岗岩的含锡热液受早期沉积(火山沉积)作用所形成的层状硫化物的“地球化学障”作用的控制而沉淀成矿。因此,大厂锑石—硫化物多金属矿床是另一种意义的沉积—(花岗岩)热液迭加改造型矿床。

GEOLOGICAL FEATURES AND ORE-FORMING MECHANISM OF THE DACHANG STRATABOUND CASSITERITESULFIDE-POLYMETALLIC DEPOSIT, GUANGXI

Dachang cassiterite-sulfide-polymetallic deposit lies in the Hercynian Indosinian fault depression adjacent to the margin of the Jiangnan geoanticline. It is a stratabound ore deposit. (1) Main ore bodies are controlled by sedimentary strata and their wall rocks consist of Late paleozoic carbonates, siliceous rock formations, and reefs. (2) Main ore bodies occur as stratoid bodies, remaining persistent in thickness and extending along the strike and dip for long distances. They were folded synchronously with the strata. (3) The stratoid bodies retain some sedimentary features, including lamination, banding, bedding convolution, boudinage-like, plicated, and residual organic structures. (4) Volcanic materials can be found in the ore-bearing strata of the minind area and its vicinity. (5) Background values of tin, lead, zinc and copper in the ore-bearing strata are high. (6) Co/Ni ratio of pyrites in stratoid bodies is less than 1.On the other hand, Dachang tin deposit is related to Longxinggai biotite granitic body which is formed in Late Yanshanian. The granitic body falls into continental transformaion type. The tin contents of the granite are high (14ppm); hence this granite is obviously a tin-bearing rock. The above-mentioned characteristics indicate that ore-forming materials of Dachang tin deposit are derived from different sources. Tin mineralization is mainly related to the granite, but most zinc, copper, lead and antimony sulfides are principally of sedimentary origin. It is reasonable to consider that Dachang tin deposit is mainly a stratabound tin deposit formed by exhalative sedimentation of sulfides with hydrothermal superimposition of tin derived mainly from the granite. The presence of strataform sulfides (originally mainly FeS_2) provides the strongly-reduced environment for deposition of tin from hydrothermal solution. So these sulfide layers may have played a role of "geochemical barrier" in ore-forming processes.