五子骑龙矿床——被改造的斑岩铜矿上部带

THE WUZIQILONG COPPER DEPOSIT—THE REFORMED UPPER PART OF A PORPHYRY COPPER DEPOSIT

五子骑龙矿床产于紫金山矿田的一个早白垩世火山管道旁侧。火山管道中充填的英安斑岩向深部逐渐相变为花岗闪长斑岩。由于后期断裂的破坏，该花岗闪长斑岩及其矿化系统被上冲到与五子骑龙矿床相邻的中寮矿床近地表位置，从而形成斑岩型铜矿床－中寮矿床。五子骑龙矿床中，环绕英安斑岩发育明矾石化、迪开石化、埃洛石化和红柱石化蚀变，这些蚀变是改造并叠加早期绢英岩化蚀变的结果。其铜矿石中的铜蓝、硫砷铜矿和蓝辉铜矿。

The Wuziqilong deposit adjacent to the Zhongliao copper deposit occur on the side of an Ear- ly Cretaceous volcanic pipe filled with dacite porphyry.From the higher level downward,dacite porphyry gradually changes into granodiorite porphyry.The granodiorite porphyry was cut by postmineral faulting and upthrusted to the place near the surface of the Zhongliao deposit.Potas- sic,phyllic and propylitic alterations surround the granodiorite porphyry,and veinlet-disseminat- ed Cu-(Mo)-mineralization composed of pyrite,chalcopyrite,bornite and molybdenite occurs in phyllic alteration zone,forming typical porphyry type alteration and mineralization.The Wuziqi- long deposit is characterized by superimposed alterations and mineralizations.From the upper to the lower part of the deposit,alunitic,dickitic,halloysitic(halloysite+diapore)and andalusitic (andalusite+diapore)successively replaced phyllic alteration and were superimposed upon it, forming an alteration zonation around the dacite porphyry.The andalusitic and phyllic alteration zone of the Wuziqilong deposit is linked downwards with the phyllie alteration zone of the Zhongliao deposit.Copper orebodies as veins mainly fill the alunitic and phyllic(Alu+Ph)al- teration zone.In ores,chalcopyrite and bornite are replaced generally by covellite,enargite and digenite. Detailed geochemical sampling reveals an element zonation of Au(Ag,Cu)-Cu(Pb, Zn)-Cu-Mo from the upper part of the Wuziqilong deposit to the depth of the Zhongliao deposit. Fluid inclusion and oxygen-hydrogen isotope studies indicate that three types of fluids exist in the deposits.The first is high temperature and high salinity fluid which comes from magmatic water and results in potassic alteration.The second,characterized by moderate to high temperature and salinity,is a mixture of magmatic water and meteoric water that leads to phyllic alteration and porphyry copper mineralization.The third fluid,characterized by acid and lower temmperature and salinity,is derived from water-rock exchange under higher water-rock ratio value.This fluid is superimposed on porphyry copper alteration and mineralization from lower part upward through transformation,forming acid-sulfate type alterations and mineralization of the Wuziqi- long deposit. Evidence mentioned above suggests that the Wuziqilong deposit represents the partly re- formed upper part of the deep Zhongliao porphyry copper system.Rb-Sr isochron and K-Ar dat- ing yielded ages of 105×10~6 a,103×10~6 a and 100×10~6 a for granodiorite porphyry,potassic al- teration and alunitic alteration respectively.