粤西阳春盆地合水金矿区煌斑岩地球化学特征及其成矿意义

Geochemical Characteristics and Metallogenic Significance of the Lamprophyrein Heshui Gold Deposit,Yangchun Basin,Guangdong Province

粤西阳春盆地合水金矿在空间上与煌斑岩具有密切的联系,金矿化主要产于蚀变的煌斑岩及砂岩的构造破碎带中。岩矿鉴定表明,本区煌斑岩的矿物成分主要由黑云母斑晶及长石组成,属于云煌岩类。云煌岩具有高硅、高钾特征,SiO_2含量平均为56.86%,K_2O含量平均为6.33%,属高钾质粗安岩系列煌斑岩。蚀变煌斑岩与新鲜云煌岩的化学成分对比表明,随着蚀变作用的进行,表现为全碱含量的显著降低和全铁含量的显著增加。蚀变煌斑岩与新鲜云煌岩的微量元素对比表明,在本区的热液蚀变过程中伴随有热液成矿元素的明显富集,其中CuBi-Sb-W-Cd的异常微量元素组合特征可以作为本区金矿化蚀变与找矿的标志性伴生元素组合。区内煌斑岩稀土元素具有总量高,LREE显著富集,HREE强烈亏损的特征,配分曲线为明显的右倾型。本区新鲜云煌岩的Au含量较低,其提供Au来源的可能性较小,但煌斑岩破碎带为成矿提供了十分有利的空间环境。本区的金矿化主要是由后期热液蚀变作用所致,其成因很可能与外围的花岗岩浆活动有关。

The Heshui gold deposit of Yangchun basin in the western Guangdong province is closely associated with the lamprophyre spatially, and gold mineralization of this deposit is mainly produced in the altered lamprophyre and tectonic fracture zone of sandstone. Rock and mineral identification reveals that the lamprophyre is mainly composed of biotite-phenocryst and feldspar, belonging to minette. Minette has high silicon and high potassium,SiO2 content of an average of 56.86%, K20 content of an average of 6.33~, which belongs to high-potassium lamprophyre of trachyandesite series. Compared to the chemical composition of fresh lamprophyre, the altered lamprophyre shows a significant reduction and increase in alkali and iron content respectively, with the proceeding of altered process, while the comparison of the trace elements shows that hydrothermal metallogenic elements have been significantly enriched in the process of hydrothermal alteration. The special combination of trace elements Cu-Bi-Sb-W-Cd can be used as a symbolic elements combination in searching for gold metallogenic alteration and prospecting in this region. The rare earth elements of the lamprophyre are enriched, characterized by LREE significantly enriched, HREE de- pleted, and the distribution curve is obvious rightward type. Although fresh lamprophyre is less likely to provide Au because of the low content of Au in Heshui gold deposit, the lamprophyre fracture zone provides an advantageous metallogenic space. The gold mineralization in this area is mainly caused by the later hydrothermal alteration, and is likely to be related to the circumjacent granite magma activity.