Study on adakitic rock and Cu-Au mineralization.

Recent work shows that there is a close relationship between adakite and Au-Cu-Mo epithermal deposit and porphyry copper deposits. Our research results obtain following opinions: ( 1 ) most of porphyry copper deposits in China are specially and temporily related to adakites, such as Dexing in Jiangxi, Shaxi in Anhui, Duobaoshan in Heilongjiang, Wunugetushan in Inner Mongolia and Tuwu in eastern Xinjiang. Some of porphyry copper deposits, e. g. , Yulong in Xizang, are originally considered to be related to be hosted by alkaline - rich intrusive rocks or A-type granites, the rocks also have adakitic affinity in geochemistry. (2 ) The gold deposits in the North China are mostly related to adakites, typical cases are those occurred in eastern Shandong Province and Xiao Qinling. (3) The country rocks of Cu-Au-Mo deposits in the middle and lower Yangtze River are mostly adakites. The reason why adakites and mineralization have such a close relationship is that they have similar conditions from the deep crust, which provides a new idea exploring Au-Cu-Mo deposits. Adakitic magma is produced when basalt is partially melted at high - pressure, high - temperature and fluid - rich conditions, which is favorable for metal elements like Cu, Au and Mo to dissolve into melts. The point is the dehydration reaction occurs when hornblende is replaced by garnet during the formation of adakitic magma, which is helpful for the dissolution of Au, Ag, Fe, Cu and Mo from basic rocks and mantle. The regions with adakites development is therefore a potential prospecting area, and the regions occuring slab-related adakite is more favorable for the enrichment of ore-forming elements. So a large potential exploration area in China is the Palaeo-Asian Ocean Orogenic Belt of late Proterozoic-Paleozoic, because subduction was widespread in the belt at that time and future exploration should be fucused on adakites and surrounding geological bodies.