关键词: 壳幔相互作用, 夕卡岩矿床, 成矿过程, 中生代, 皖赣沿江地区

Abstract:

A large number of Mesozoic intrusions, their enclaves and related skarn ore deposits are distributed along the Yangtze River.We present thirty years of our study on Mesozoic intrusions with xenoliths and associated skarn deposits in the Jiangxi-Anhui segment along the Yangtze River. Specifically, this paper focuses on the analysis of the Mesozoic crust-mantle interaction and metallogeny of various skarn deposits in the area in order to lay some foundation for the development of crust-mantle metallogeny. Isotopic chronological and petro-geochemical data of the basic intrusive rocks and mafic xenoliths confirm the occurrence of underplating of the post-collisional mantal-derived magma (145-135 Ma) rich in Cu and Au, and the post-orogenic mantal-derived magma (130-120 Ma) rich in Fe and Au. In addition, the existence of similar activities of magma from the mantle with crust in the Mesozoic can be confirmed from the data. The activities of magma from the mantle with crust mainly include crystalline fractionation, assimilation and contamination, magma mixing, and magma liquation. Geological investigation and microscopic observation of skarn deposits show that the two episodes of intrusions of various mantle-derived magmas with crust into Late Paleozoic to Early Mesozoic wallrock strata led to mineralization of various skarns responsible for the formation of various skarn deposits, including contact replacement, stratabound, magma, and compound and superimposed skarn deposits. These deposits are characterized by distinct types of mineral assemblage and texture as well as the structure of hydrothermal replacement, sedimentation-hydrothermal replacement, magma crystallization-hydrothermal replacement, and sedimentation-magma crystallization-hydrothermal replacement, respectively. The existence of the xenoliths of Proterozoic metamorphic rocks, rich in ore-forming materials such as Cu and Zn in the post-collisional acidic to intermediate-acidic intrusions, supports contamination of the Proterozoic metamorphic basement in the shallow-level magma chamber by the post-collisional underplating basaltic magma rich in Cu and Au or its evolved magma. The contamination resulted in Cu further enrichment to form acidic to intermediate-acidic magmas with increased Cu. The occurrence of the cumulates containing a lot of Cu-Fe sulfides (chalcopyrite and pyrrhotite) and oxide inclusions in the post-collisional intermediate-basic to basic intrusions, is consistent with intensive crystalline fractionation of the post-collisional underplating basaltic magma rich in Cu and Au and its evolved magma in the deep-level and shallow-level magma chambers, respectively. The crystalline fractionation caused depletion in Cu and Fe to form intermediate-basic to basic magmas with even higher Au enrichment. Text Some skarn enclaves occur in the post-collisional acidic to intermediate-acidic intrusions, and few enclaves of the transition of gabbro to skarn exist in the skarn. This fact indicates the contamination of the Late Paleozoic carbonate strata with Cu and Fe source bed by the post-collisional underplating basaltic magma rich in Cu and Au in the intrusive location, leading to Cu further enrichment to form a skarn magma with increased Cu. The acidic to intermediate-acidic magmas with increased Cu, the intermediate-basic to basic magmas with increased Au, and the skarn magma with increased Cu are the most important controlling factors for the formations of contact replacement and stratabound skarn Cu, contact replacement skarn Au, and magmatic skarn Cu ore deposits during the post-collisional period, respectively. The occurrences of the deep-level and shallow-level cumulates containing a lot of Cu-Fe sulfides (chalcopyrite and pyrrhotite) and oxide inclusions in the post-orogenic intermediate-basic to basic intrusions provide evidence for intensive crystalline fractionation of the post-orogenic underplating basaltic magma rich in Fe and Au in the deep-level magma chamber. The crystalline fractionation combined with magma mixing caused depletion in Cu and Fe to form intermediate to basic magmas with higher Au enrichment. Contaminations of the Late Paleozoic carbonate strata with Cu and Fe source bed, the Early Mesozoic Fe source bed, and the Early Mesozoic Fe and Si source bed by the post-orogenic underplating basaltic magma rich in Fe and Au in the intrusive location led to Fe, Fe, and Fe and Si further enrichments to form skarn, basic, and intermediate to basic magmas more enriched in Fe, respectively. The intermediate-basic to basic magmas with increased Au enrichment as well as the skarn, basic, and intemediate-basic to basic magmas with increased Fe enrichment are predominantly responsible for the formation of contact replacement skarn Au, magmatic skarn Fe, ore magma Fe, and contact replacement skarn Fe ore deposits during the post-orogenic period, respectively.

Key words: crust-mantle interaction, skarn ore deposit, mineralization process, Mesozoic, Anhui-Jiangxi segment along the Yangtze River