高级矿床学找矿案例斑岩矿床.ppt

高级矿床学-斑岩型矿床 斑岩铜矿 Genesis Thought to be a two stage model (Figure). Emplacement of shallow plug-like stock in the vent of a felsic stratovolcano. Magmatic-meteoric water system develops as igneous activity wanes causing pervasive alteration and the disseminated tin mineralization. As temperature declines cooling causes fracturing of the rocks. These fractures widen and deepen eventually tapping the deeper magma chamber feeding the volcano. This allows volatiles to escape the chamber and stream upward. Cooling causes deposition on fracture walls generating the vein-type tin mineralization. Characteristics of Porphyry Cu-Mo-Sn Deposits 1Restricted to the Phanerozoic (mostly Mesozoic-Tertiary). Closely associated with felsic intrusives of qtz diorite to qtz monzonite composition. 2Accompanied by characteristic alteration envelope. potassic-- phyllic-- argillic-- propylitic. 3Strong zoning in relationship to plate boundaries. Cu Mo Sn moving inland from the plate margin. 4Closely associated with island arc development and subduction zones at convergent ocean-continent plate boundaries. 5Ore occurs in a large, low-grade shell adjacent to the potassic zone. Chalcopyrite and bornite most common minerals with lesser molybdenite and cassiterite. 6Isotopic evidence suggests shallow depths of magma generation and significant groundwater interaction. Vein-type Deposits These were once one of the most sought after and heavily mined types of ore deposits. The famous mining districts of the West are mainly vein-type deposits. Vein-type deposits represent a progression into true hydrothermal deposits that lie at some distance from the igneous source. Today this group has declined markedly in importance, but still produces much of the world’s silver and tungsten and some gold and base metals. The search for this type of deposit has been abandoned largely because they tend to be small and difficult to find. Lindgren Classification - Still much in vogue for the description o