Abstract;Porphyry-style gold deposits, defined primarily by large-scale tonnage (50Mt-1000Mt) and low-grade (0.5-2g/t: Au), are represented by more elevated gold contents when compared with porphyry-style copper deposits. In addition to their significant economic contribution, an extensive zonation pattern in alteration and mineralization in porphyry-style gold deposits have become important research objectives serving as clues to trace the genetic linkage of magmatic intrusions and their associated hydrothermal systems, incorporating the porphyry-style copper deposits and epithermal ore environments. Based on reviews of the latest better-documented research with particular emphasis on morphology and fluid evolution in porphyry-style gold deposits in the Maricunga belt of Chile and other porphyry-style deposits, the controlling factors for gold and copper contents in porphyry-style deposits are examined. Assuming mineralized fluids separated from the same initial composition of magmatic intrusions, Cu/Au ratio of porphyry-style deposits is considered to be controlled first by depth, where intrusion emplaced while accompanying fluid immiscibility, and second, by the highest temperature of immiscibility for mineralized fluid derived from magmatic intrusion. But it also depends on the evolution of hydrothermal system involving boiling and/or flashing events. A recommended threshold pressure (ca. 0.5kb) and temperature (ca. 500.DEG.C.) will lead to the mineralized boiling fluid dividing into porphyry gold deposits at lower pressure and higher temperature and porphyry copper deposits at higher pressure and lower temperature. This index may provide an exploration tool for identifying the Cu/Au ratio of porphyry-style deposits. (author abst.)