Abstract:

The Copiapó GV area of northerncentral Chile is situated in the transition zone between a Mesozoic iron oxide coppergold (IOCG) deposit and a porphyry copper deposit. The intrusive rocks mainly consist of calcalkaline, medium to coarse grained gabbro diorite, diorite, diorite porphyry, biotite granite, porphyritic granite and monzonite. These rocks are classified into the category of calcalkaline, Itype and magnetite types, which is derived from the upper mantle. The assemblage of the intrusive rocks is interpreted to be formed at the subduction zone of oceanic crust during conversion from partially expansion to extrusion. As a consequence, the Mesozoic backarc basin closed up and uplifted rapidly. The magma intruded mainly in the period of Late CretaceousPaleocene (about 65-54 Ma). The magmatic activities of different periods created a number of hydrothermal centeres and developed horizonal alteration zones and veintype alterationmineralization zones. On surface argilizationchlorite alteration, porous and silicified stockwork, and AuAg bearing FeMn carbonate stockwork well developed. The widely extensive alteration zones contain gold, silver polymetallic veins, which may indicate that the area could develop some epithermal AuAg polymetallic deposits. These phenomena may present the potential of occurrence of IOCG mineralization or porphyry coppergold mineralisation in deep area. Further study of alteration and mineralization should be strengthen, which will create a guideline of exploration for the deepburied deposits in the future.

Key words: Chile, IOCG deposit, intrusive rock, petrological geochemistry, chronology