Spatial-temporal heterogeneity of magma emplacement process and its constraints on localization of associated orebody: A case study in the Shizishan orefield of the Tongling Ore Cluster, East China

摘要

We present a study on the Dongguashan quartz diorite stock which is the largest Early Cretaceous intrusion associated with skarn-porphyry polymetallic ore deposit in the Tongling Ore Cluster, Middle-Lower Yangtze Metallogenic Belt in East China. The Dongguashan quartz diorite show massive texture without obvious foliation, and intrusive contact was locally observed inside of the stock. The anisotropy of magnetic susceptibility (AMS) results of the stock show two distinct groups. The Group I (G-I) is dominated by NE-SW-striking magnetic foliation with variably oriented magnetic lineation. The Group II (G-II) that intruded into G-I is characterized by steep NW-SE-striking magnetic foliation and lineation, which are parallel to the vein-like orebody developed in the stock. The 3D geometrical modelling of the stock displays a triangular shape in plan-view with an eastward bulge and irregular stock boundary in the eastern side and the contact surface is steeper in the west than that in the east, denoting that the stock was constructed with an eastward magma accretion trend. Furthermore, the Dongguashan quartz diorite has a wide range of composition and geochronological data, suggesting a multiple magma pulses emplacement model. Accordingly, we propose that the Dongguashan stock was constructed by at least two stages magma pulses. The earlier stage magma pulses intruded along the NE-SW-striking preemplacement structures in the country rock and partly intruded into the lithological and mechanical discontinuous interfaces which yielded the stratabound skarn orebody. The eastward magma accretion produced a highly deformed and longer heated country rock on the eastern side of the stock, favoring the orebody development along the eastern stock-country rock contact interface. The late-stage magma pulse and the parallelism among the trend of magnetic foliation of G-II, extensional structure and vein-like orebody suggest that the veintype orebodies may controlled by both magma emplacement and regional tectonics.