Abstract:The correct description of alteration and mineralization at top and root zones of porphyry copper system proves to be essential for the assessment and exploration of the pipe-shaped porphyry deposit. Some geologic features of root zone of the Zhongteng porphyry copper (molybdenum) deposit, a typical deposit of this kind in the coastal volcanic rock belt of southeast China, are presented in this paper. The ore-related porphyry is late Yenshanian hypabyssal quartz diorite- porphyrite dike with K-Ar ages of 101.9-116 m. y. The petrological and petrochemical data, isotopic composition of oxygen (δ18Oquartz = 9.5‰), geochemistry of REE (δEu=0.53) and tectonic position of this porphyrite all seem to imply that the porphyrite and its ore-forming materials might be the products of differentiation and evolution of basaltic-andesitic magma generated as a result of the melting of oceanic lithosphere subducting along the continental margin beneath an adjacent plate. As most part of the original porphyry copper deposit has been worn away by erosion, the present primary ore bodies are virtually the surviving portion of this deposit, the alteration and mineralization characters of whose root zone are generalized as follows: 1. No propylitic zone has ever been found in the deposit and pyrite-sericite-quartz rocks are chiefly seen at a few hill tops nearby, in contrast, potassium silicate alteration is widely distributed, making up the major alteration type and getting more intense with depth. 2. The prospected primary ore bodies occur mostly within the potassic zone, with chalcopyrite, molybdenite, pyrite and, to a less amount, magnetite and pyrrhotite as their associated metallic minerals. On the other hand, galena and sphalerite, frequently found at the top of the porphyry copper system, are rarely observed in the deposit. Zinc content of primary ore is extremely low——not exceeding the permissible content of harmful elements and impurities. 3. Molybdenum mineralization is commonly believed to persist to a greater depth than copper mineralization, Primary molybdenum ore bodies have been noticed beneath copper ore bodies in this deposit. 4. The surrounding rocks of the deposit-Zhongteng quartz diorite mass——has relatively distinct zoning of petrofacies. Groundmass of quartz-diorite porphyrite is minute- or fine-grained in texture. These characters furnish evidence for the claim that the Zhongteng deposit is actually the root zone of an upright porphyry type mineralized rock pipe.
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杨世义，刘媚群，张秀兰，陈长江.1984.福建钟腾斑岩铜（钼）矿床根带的蚀变矿化特征[J].矿床地质,3(1):12~18.1984.Alteration and mineralization at the root zone of the Zhongteng porphyry copper (molybdenum) deposit in Fujian Province[J].Mineral Deposits3(1):12~18
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