粤北新洲逆冲推覆断裂系统中断层岩的地球化学特征

GEOCHEMICAL CHARACTERISTICS OF FAULT ROCKS IN NAPPE-FAULT SYSTEM OF THE XINZHOU NAPPE STRUCTURE, NORTHERN GUANGDONG, CHINA

粤北新洲逆冲推覆断裂系统由Ⅰ、Ⅱ、Ⅲ～Ⅳ级推覆断层带组成,断层带中形成一套复杂的断层岩系,断层岩中Au、Pb、W、Sb、Bi、Hg普遍富集,由此引起不同程度的金矿化,分别形成石英碳酸盐糜棱岩型金矿、碎裂钠长石岩型金矿和石英脉型金矿,成矿时期为印支晚期至燕山期。通过系统的微量元素、同位素(Pb、S、C、H、O)和流体包裹体研究表明,Ⅰ级推覆断层带断层岩中的成矿物质主要来自下地壳或上地幔,Ⅱ级推覆断层带断层岩中的成矿物质部分来自地壳深部,部分来自外来系统震旦系地层,而Ⅲ～Ⅳ级推覆断层带断层岩中的成矿物质则主要来自外来系统震旦系地层,并由同推覆期动力分异热液所携带。

The nappe-fault system of the Xinzhou nappe structure in northern Guangdong Province is composed of Ⅰ -order(F_Ⅰ), Ⅱ-order(F_Ⅱ ) and Ⅲ～Ⅳ-order(F_(Ⅲ～Ⅳ)) nappe-fault zones, in which a series of fault rocks were formed . The different types of fault rocks in the Ⅰ -order, Ⅱ-order and Ⅲ～Ⅳ-order nappe-fault zones are all enriched in Au, Pb, W, Sp, Bi, Hg, which led to the well-developed Au mineralizations and formation of quartz-carbonate mylonite, Cataclastic albite rock, and quartz-vein gold deposits, respectively. The Au-mineralization took place in Late Indosinian Orogeny and Yanshanian time. The downward Au-mineralization sequence in tectonites in the nappe-fault zones is F_(Ⅲ～Ⅳ)→F_Ⅱ→F_Ⅰ. Furthermore, Pb, S, C, H, O isotopes in the fault rockof F_Ⅰ are all hypogenic showing that ore-forming materials such as Au in F_Ⅰ were derived mainly from the upper mantle or the lower crust and removed in the form of M^+(AuS_2)^- or Au (HS)_2^-, while Pb, S, C, H, O isotopes in the fault rocks of F_(Ⅲ～Ⅳ) are all of upper crust type, and commonly consistent with those in the metamorphosed Sinian strata in the nappe. It means that ore-forming materials such as Au in F_(Ⅲ～Ⅳ) were derived mainly from the metamorphosed Sinian strata in the nappe and removed by the dynamical differentiation hydrothermal solutions formed during the thrusting in the form of M^+(Au Cl_2) or M^+(AuCl_4)^-. In the fault rock of F_Ⅱ, Pb and part of C isotopes are hypogenic, but S, H, O, and part of C isotopes were derived from sediments. It indicates that the ore-forming materials such as Au in F_Ⅱ were derived partly from the metamorphosed Sinian strata in the nappe and partly from the lower crust or the upper mantle.