桂西北地区古地热场特征及其在微细粒浸染型金矿床形成中的作用

THE PALEOGEOTHERMAL FIELD OF NORTHWESTERN GUANGXI:CHARACTERISTICS AND ITS ROLE IN THE FORMATION OF MICRO-DISSEMINATED GOLD DEPOSITS

本文以右江盆地古地热场特征分析为基础，并结合岩相和构造研究的成果，提出了沉积盆地中微细粒浸染型金矿床形成的古地温控制模式：即海底火山喷发和还原的沉积环境条件对成矿物质初始富集的控制，盆地的构造深沉降引起古地温升高促使含矿流体形成、运移和圈闭，盆地的后期构造活动和抬升引起含矿流体层的破裂或降温，致使含矿流体突破、淀析成矿。

Using vitrain reflectance data , the author made a fairly systematic inve-stigation into the paleogeothermal field characteristics of Late Permian andEarly Triassic strata beneath the maior auriferous horizon of northwesternGuangxi-Middle Triassic.The results show that the Late Permian and EarlyTriassic strata had been under the rather high geothermal condition beforethe uplifting of the basin,and the paleogeotemperature could reach 250～300℃, with the existence of a high paleogeothermal gradiemt zone betweenthem and Middle Triassic strata,Based on an analysis of tectonic evolutionand sedimentary facies distribution in the basin, the paper describes theimportant role played by the paleogeothermal field in the formation ofmicro-disseminated gold deposit,and points out the combinational relationsof gold source bed , deposits-forming bed and capping bed. On such a basis,the metallogenic mechanism of gold deposits in this area might be dividedinto three stages :①the early stage of the basin, during which regionalmagmatic activities and organism-rich reductive sedimentary facies createdfavorable conditions for the formation of the source bed;②the rapid deepsubsidence stage of the basin,during whicb the capping bed was formed,and the temperature of the source bed gradually rose;when the subsidencereached the depth of over 4000 m,the ore-bearing hot fluids came into beingand migrated, forming the closed system of the ore-bearing hot brine at thefavorable positions;③the late stage of the basin :due to the uplifting ofthe basin and the faulting, the temperature of the ore-bearing hot brinetrap got lower and lower,and breakthrough took place along the stress reliefbelt; as a result,ore-forming materials were unceasingly separated out,eventually leading to the formation of ore deposits.