江西银山铅锌铜矿化机制的讨论

本文分析了银山矿区所处的火山盆地边缘这一特定地质构造环境,火山活动的多阶段性以及蚀变矿化的基本特征,指出在银山发生过两期矿化作用,分别对应于两个阶段的火山-次火山活动。第一阶段的流纹英安质次火山活动产生铅锌银矿化,第二阶段英安质次火山活动则伴随铜(铅锌)矿化。因此,作者认为银山铅锌铜矿床是典型的次火山热液矿床,是两期矿化叠加的结果,从而对前人关于银山矿的成因模式和归类提出了异议。本文还对银山矿与德兴斑岩铜(钼)矿田的成因联系问题提出了独特的看法,并指出了银山式铅锌(铜)矿化的找矿方向。

A Discussion On The Mechanism Of Lead, Zinc And Copper Metallogeneses In Yinshan, Jiangxi Province

Located in the northeast margin of the Lehua-Dexing Mesozoic volcanic deposit is a subvolcanic type hydrothermal deposit closely related to the early Yanshanian intermediate-acidic volcanic-subvolcanic rocks. Three major stages of magmatic activities, which are from early to late rhyodacitic, dacitic and andesitic respectively, have been recognized in Yinshan by lots of researchers. Each stage started from eruption of pyroclastic materials, then went through lava extrusion, and ended with emplacement of subvolcanic rocks such as dikes and small stocks. The eruption order of the three volcanic stages reveals a well preeruption differentiation of magma in the magma chamber, which is of great significance to the related Pb, Zn and Cu mineralization. The Yinshan deposit has long been considered as a porphyry type deposit and as a product of associated mineralization of the well-known Dexing porphyry copper system which conforms with the model of R. H. Sijlitoe. The metallogenic mechanism bas been described as an axial symmetric zoning of hydrothermal alteration and mineralization from No.3 dacite porphyry dike both southward and northward. This dike, belonging to the subvolcanic facies of the second volcanic stage, has thus been supposed to be the mother rock of Pb, Zn and Cu mineralizations. On the basis of an analysis of such geologic aspects of Yinshan area as the basic tectonic setting, the distribution of volcanic rocks of different stages, and the multiple episodes of hydrothermal alteration, a new opinion is proposed in this paper that the Yirrsban Pb-Zn-Cu deposit was formed as a result of the superimposition of two metallogenetic episodes. The first episode was the mineralization of Pb, Zn, (Ag), related directly to the first stage subvolcanic rocks, mainly thyodacite porphyry dikes. The center of this mineralization was at the northern sector of Ymshan with the ore fluid migrating mainly southward. The second one was mainly Cu mineralization and resulting from the second stage subvolcanic activities such as No. 3 dacite porphyry dike. The overlapping of the latter mineralization on the former has Jed to the formation of the present feature of the Yinshan deposit. This mechadism is also supported by some other charactecs of mineralization, such as ore body shapes, mineral assemblages and the distribution of metallic elements. Furthermore, the author argues in the paper that as there exist distinct differences in time and tectonic setting between the Yinshan deposit and the Dexing porphyry copper deposit, these two deposits are unlikely to be products of one mineralization process.