我国一些重要夕卡岩Pb-Zn多金属矿床的交代分带

METASOMATIC ZONING IN SOME MAJOR Pb Zn POLYMETALLIC SKARN DEPOSITS OF CHINA

在我国一些重要夕卡岩Ｐｂ－Ｚｎ多金属矿床中，交代矿化分带十分明显，主要表现为围绕侵入体接触带或热源中心向碳酸盐围岩方向，呈现有规律的带状分布。根据有关岩浆岩和矿化组合的不同，可大致划分为三个交代分带序列，总的分带序列是：Ｆｅ（Ｍｏ）→Ｆｅ－Ｓｎ→Ｓｎ（Ｗ）－Ｃｕ→Ｃｕ－Ｚｎ→Ｚｎ、Ｐｂ（Ａｇ）。其中Ｆｅ、Ｍｏ、Ｓｎ、Ｃｕ矿化主要与镁夕卡岩或钙夕卡岩有关，而Ｚｎ、Ｐｂ（Ａｇ）矿则总是与锰（钙）质夕卡岩伴生。上述分带序列是寻找隐伏矿床（体）的重要标志之一。

Metasomatic zoning in some major Pb Zn polymetallic skarn deposits of China is very clear. From the contact zone of igneous rocks or the center of a heat source to carbonate wall rocks, there roughly exist three zonality sequences:① Granitoids→K feldspathized (partially basic plagioclased) granitoids→calcic skarn (+cassiterite, magnetite, sphalerite)→calcic skarn(+chalcopyrite, sphalerite)→manganoan skarn(+sphalerite, galena, argentiferous minerals)→marble (Haobugao and Baiyinnuo, Inner Mongolia);② Quartz diorite→altered quartz diorite→magnesian skarn(+magnetite+molybdenite)→calcic skarn(+magnetite, pyrite and pyrrhotite)→Manganoan skarn (+sphalerite, galena and argentiferous minerals)→dolomitic marble (Bajiazi, Liaoning);③ Diabase diorite→basic plagioclased diabase diorite(+molybdenite)→calcic skarn(+magnetite, +magnetite)→manganoan skarn (+sphalerite and galena)→marble(Makeng and Dapai, Fujian). As a result of K feldspathization or basic plagioclasization of igneous rocks in the endocontact, magnetite and mafic minerals(hornblende or biotite) have decomposed, forming distinct light colored metasomatic zone. Different types of skarns are closely related to respective mineralizations. Fe(Mo), Sn, Cu mineralizations are related to magnesian or calcic skarns, while Pb Zn(Ag) mineralizations are invariably accompanied by manganoan skarns. Investigation of fluid inclusions of minerals reveals that from the contact zone to carbonate country rocks, the forming temperatures of the ore bearing skarns are reduced gradually in order of magnetite bearing calcic skarn(600～400℃)→Sn(Cu,Zn) bearing calcic skarn(450￣327℃)→manganoan skarn with Pb Zn(Ag) mineralization (400￣200℃). Systematic study of oxygen and sulfur isotopes of pyroxene and sphalerite from different metasomatic zones of the Baiyinnuo deposit shows that from the center of the heat source to the carbonate wall rocks, δ 18 O values of pyroxenes and δ 34 S values of sphalerites obviously decrease, with even the appearance of clear negative values in the Pb Zn(Ag) bearing manganoan skarn zone( δ 18 O-5 9～12 4‰, δ 34 S-5 1%～-6‰),which indicates the participation of a lot of meteoric water in the course of lithogenesis and mineralization.