塔前–赋春钨铜多金属矿集区构造–岩浆–成矿作用

塔前–赋春矿集区内近年来新发现了世界最大的钨铜多金属床(朱溪),引起了业界同行的广泛关注。在已有研究资料和最新勘探成果的基础上,本文对矿集区内成矿地质条件、矿床类型及成矿规律、构造–岩浆–成矿作用进行了系统总结和论述。结果表明塔前–赋春矿集区内自晋宁期以来经历了多期构造–岩浆活动,钨铜多金属矿床主要与燕山期构造–岩浆活动关系密切。矿床类型主要有矽卡岩型、斑岩(蚀变花岗岩)型和热液脉型(破碎带型)。矿床在空间上呈现出北东成带、北西成串的分布特征。区域性北东向推覆构造带控制了区内矿床展布,而逆冲推覆构造、不整合界面、岩体接触带、张裂构造、层间裂隙及破碎带则直接控制了矿床的形成及矿体的空间就位。

Geochemistry of intrusive rock in Dachang tin-polymetallic ore field, Guangxi, China: Implications for petrogenesis and geodynamics

The major element, trace element and rare earth element（REE） of the intrusion rock from the Dachang ore field in Guangxi, China, were analyzed. The results show that the phenocryst（about 15%） and matrix（about 85%） mainly consist of quartz, K-feldspar and plagioclase. The rock is composed of low content of Si and high content of Al2O3, low contents of Ca, Fe2O3, Na, TiO2, etc. The intrusion rock has the medium alkali content, attributing to K-rich type rock; and contains medium to low REE contents, of which light rare earth elements（LREEs） and heavy rare earth elements（HREEs） are highly fractionated, showing a weak negative Ce anomaly and a negative Eu anomaly. These rocks are enriched in LREE, and the large ion lithophytes elements（LILE） are rich in Rb, Sr, and U; the high-field-strength elements（Nb, Th, etc） are relatively depleted. The REE chondrite-normalized patterns are consistent with the overall, roughly indicating their similar characteristics, sources and evolution. The intrusion rock mainly formed during the collisional and within-plate periods.

Late Mesozoic magmatism and tectonic evolution in the Southern margin of the North China Craton

Late Mesozoic granitic magmatism(158–112 Ma) are widespread in the southern margin of the North China Craton(NCC), contemporary with many world-class Mo-Au-Ag-Pb-Zn polymetallic deposits. There are abrupt changes in the elements and isotopic compositions of these granites at about 127 Ma. The early stage(158–128 Ma) granites show slightly or no negative Eu anomalies, large ion lithophile elements enriched and heavy REE depleted(such as Y and Yb), belonging to typical I-type granite. The late stage(126–112 Ma) granites are characterized by A-type and/or highly fractionated I-type granite, with higher contents of SiO2, K2 O, Y, Yb and Rb/Sr ratio and lower contents of Sr, δEu value and Sr/Y ratio than that of the early-stage granites.Moreover, the whole rock Nd and Hf isotopic compositions of the granites younger than 127 Ma show more depleted than those of the older one. The two stages of Late Mesozoic granites were derived from a source region of the ancient basement of the southern margin of the NCC incorporated the mantle material. The late stage(126–112 Ma) granites contain more fractions of mantle material with depleted isotopic composition than the early ones. The granites record evidence for a strong crust-mantle interaction. They formed in an intracontinental extensional setting which was related to lithospheric thinning and asthenospheric upwelling in this region, which was possibly caused by westward subduction of the Paleo-Pacific plate. 127 Ma is an critical period of the transformation of the tectonic regime.