甘肃礼县杜沟金矿床地质地球化学特征及成因分析
Geologcal-Geochemcal Features and Genesis of Dugou Gold Deposit of Li County, Gansu Province
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摘要: 杜沟金矿床位于秦岭华力西褶皱带北亚带西段,赋存于中川岩体外接触带的李坝群中,受岩体和断裂双重控制.矿床自然类型为构造蚀变岩型金矿,矿床规模已达大型.笔者从赋矿地层,控矿构造,脉岩与成矿关系、矿石特征、围岩蚀变等方面阐述了矿床地质特征.并通过对成矿流体、稳定同位素、稀土元素的研究,阐明了杜沟金矿床的地球化学特征.以及对同位素地球化学的研究表明,硫同位素δ34S变化范围小,均一性强,显示与中川花岗岩体侵入活动有关.氢氧同位素在δD-δ18O图上投落在岩浆水和大气水之间,说明成矿热流体为混合热液.铅同位素研究属铀铅混染形成的异常铅,中川花岗杂岩体为一富铀岩体,说明成矿与中川岩体有一定的成因联系.根据铅同位素、锶同位素测定结果,杜沟金矿的主要成矿期为燕山早期(171.6~173.4Ma)与中川岩体的成矿年龄接近(181.5~219Ma).中泥盆李坝群在其沉积成岩过程中形成金的初始富集.断裂构造控制着金矿的分布与定位,岩浆岩是成矿的重要热动力源,是金矿形成的主导因素,也是成矿的必要条件.沿断裂形成的富含成矿物质的热卤水,最终富集成矿.矿床成因类型为岩浆期后热液和地下热卤水溶滤复合型金矿床.岩体周围1~5km构造热动力叠加改造的矿源层是最佳的成矿找矿地区.对矿床地质地球化学特征及成因进行探讨,对甘肃境内礼(县)—岷(县)成矿带上寻找同类型矿床有一定的指导意义.Abstract: Controlled by plutons and faults, the Dugou gold deposit is located in the western portion of the Hercynian fold belt in the Qinling Mts., and occurs in the Liba group of the outer contact zone of the Zhongchuan pluton. The natural type of the ore deposit belongs to the structure-alteration rock type. The deposit has already reaches largesize. The paper studies geological characteristics of the deposit from orebearing strata, ore-control structures, relationship of vein rock and mineralization, ore features and alteration of country rocks. Geochemistry of the Dugou gold deposit has been studied in terms of stableiso-topes, ore-forming fluids and REE. The isotopic geochemistry indicates that 34S changes in a small range and shows strong homo geneity, which is related to the emplacement of the Zhongchuan pluton. Hand O isotopes fall in between magmatic water and atmosphere water in the δD-δ18O diagram, reflecting that the ore-forming fluid is mixed ther malf luid. Lead isotopes are anom alous lead derived from mixture between U and Pb. This could be genetically in relation with the Zhongchuan pluton rich in U. From the Pb-Sriso-topic analy tical results, the main metallogenic period is inferred to be in the early Yanshan orogeny (171.6 Ma～173.4 Ma) close to that of the Zhongchuan pluton (181.5 Ma～219 Ma). The middle Devonian Liba group has Auinitial enrichment duringits deposit and diagenesis. Faults basically controlled spatial distribution and location of gold ore, while magma is anim portant thermal dynamic source and a major factor necessary for the deposit. Finally it formed the ore deposit by thermal brine rich in ore-forming materials along the faults. The genetic type for the deposit is the lixiviation composit type of post-magmatic hydrothermal and underground thermal brine. Tectono-dynamics superposed ore layers in 1～5 km range around the plut on are targets for prospecting.
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