摘要:
广西中部的来宾—武宣—象州地区是泥盆系象州型的典型地区,又发育较多的铜、铅、锌多金属脉状矿床和层状-脉状重晶石矿床。过去工作主要是对单个矿区或矿带作评价,而对各矿种间的关系,对区域中成矿作用的联系讨论较少。本文研究了该区泥盆系中的多金属矿与重晶石砂的时空关系和地球化学特征,认为是由统一的上泥盆世热水对流体系形成的热水沉积矿床。不同的矿种,矿体的不同产状由对流体系的特点和地质环境的差异所决定。
Abstract:
The centeral Guangxi Province is located in a platform which was consolidated-in Caledonian orogeny. Stratiform barite deposit (SB) and vein Pb-Zn-barite deposit (VB) occur in a rift basin in Devonian system. The Devonian lithologic units are listed here: (1) red clastic rocks of littoral and facies, (2) lutite-carbonate of neritic facies, (3) chert layer and banded limestone. The SB occurs in the chert layer in Upper Devonian system and the VB occurs in the neritic strata in Middle and Lower Devonian system. In space the VB is located in both sides of the basin, but the SB occurs in the middle of the chert layer which is 150m in thickness in the western side of the basin, and ore layer is more stable in thickness and extends up to several km. The apicall, floor and band plates of the ore layer are the chert layers. Grey and grey-black SB with banded and striped structures is composed of fine, grey barite. The section of the barite layer shows symmetricl eye shape. Composition of the SB is very simple. The radiospherical barite is located in the outside of eye structure. Fluid inclusions are very rare and very tiny, whose homogenous temperature is about 140℃, and the enclosure system is SO4-Cl-Na-K. The δ(34)S values of the barite is about +29‰. SB is associated with stratiform Mn, U, Mo mineralization. However, VB occurs in clusters containing basemetal veins (PV), basemetal-barite veins (VB) and single barite veins (MVB). The ore veins show zonation in horizontal and vertical directions. The horizontal zoning of the barite vein cluster is PV, VB, MVB outside around a deep fault controlling the rift basin, and the vertical zoning displays its feature in extended depth of the oreveins, mineralization temperature, mineral composition and country rock alteration etc. The δ_(34)S‰ values of VB are 19-30 (average 26.5), of MVB are about 23-26 (average 25.1). The enclosure system in MVB is SO4-Cl-Xa-K. VB and SB are different produces of same mineralization, the envidences are: (1) VB and SB occur in the same rift basin, and are closely associated with each other, VB is located under the SB layer, (2) ore composition, structure, texture, feature and temperature of mineralizing solution, ore-bearing country rocks (from silication rock to chert layer) and country rock alterations are similar and display obvious and systematic evolution from VB to SB,(3) the δ(54)S values of VB and SB are similar and approximated to the average value of sulfate in Later Devonian marine water, but are not similar to average value of sulfate in Early Devonian water, so that we propose a thermal water mineralization model. The study indicates the SB and country rock-chert layer are typically deposited by thermal water, so it is necessary to propose a stratiform-vein type deposit which is typical representation of thermal water mineralization.