Hunan Qianlishan Granite Constraints On Mineralization

Outcropping area of the Qianlishan granite pluton is only10km2, but the surrounding is distributed with a series of W, Sn, Mo, Bi, Be, Pb, Zn, Ag large or superlarge deposits. Over the years, many geological scholars have conducted in-depth research on this area, and many conclusions understanding reached an agreement. As for the change of temperature field and fluid field of the Qianlishan granite emplacement process, radiogenic heat, fission track analysis and so on, there is no in-depth study. Researched on the radioactive heat production, fission track, heat and mass transport numerical simulation of the Qianlishan pluton, writer mainly obtained the following understanding:1. According to the inversion of gravity data and magnetotelluric data, we abtained extension and occurrence of the deep of Qianlishan granite pluton:the Granite Emplacement depth is less than20km, which belongs to the rootless granite pluton, granite genesis to continental and crust remelting. The surface outcrop area is small but the deep concealed rock mass, Dongpo, Hongqiling, Shizhuyuan, Yaogangxian, Yejiwei metallogenic belt and so on around the huge. According to the distribution and the law of rocks mass, the rocks mass are often inferred favorable metallogenic belt.2. The average abundance of Qianlishan granite pluton Radioactive elements: U=17.01×10"6, Th=42.09×10"6, K=42.63×10-3, Rb=55.46×10-5, belongs to high heat production granite, the radioactive heat production reached4.123×1014J· a-1. The paper belives that, radioactive heat production has played an important role in extended duration of the temperature field which has an important effect on the ore-forming.3. The fission track results show that:the fission track age of zircon samples can be divided into two age groups,125-141Ma and149-165Ma. The same as the two age of Qianlishan magmatic activity. Hydrothermal mineralization lasted about45Ma (the temperature of hydrothermal mineralization between200～580℃), high temperature environment for long period provides the necessary heat for mineralization. Apatite fission track display can be divided into2age groups:28-36Ma and20-22Ma, track length for an average of11±2.2to12.8±2.2μm. Fission track sample part annealing mainly focused on50Ma-10Ma, show that due to formation of uplift and denudation, which makes the paleo temperature dropped to80℃-120℃during150Ma-50Ma. Thickness of the formation of uplift and denudation is3880m in Qianlishan area since150Ma.4. Through analysis the numerical simulation of heat and mass transport, we recognized that the temperature field of Qianlishan granite pluton in the SE direction lasted about10Ma, and the fluid field lasted about10Ma. During1Ma-10Ma, the temperature field and the fluid field overall decayed but partially strengthened, and migrated to the southeast, associated with topography and the migration of magma flow during magmatic emplacement process, the region with better metallogenic environment, it is also the Shizhuyuan, Yejiwei etc. metallogenic belt position location. The temperature field of Qianlishan granite pluton in the NE direction lasted about30Ma, and the fluid field lasted about30Ma. The temperature field and the fluid field were continuously for a long period, this long and high heating effect provided very favorable conditions for the mineral in extraction and separation, migration and accumulation of mineralization in magmatic hydrothermal, this is also the key for a series of large, super large mineral deposits to form around the rock mass.5. Qianlishan granite pluton was formed in the post collision extensional environment, cracks and fissures were relatively development, provides a good channel for migration and accumulation of ore fluid. Pluton emplacement depth is shallow, easy to form a scale hydrothermal circulation, and are rich in U, Th and other radioactive elements, belongs to high heat producion granite, multiple magma emplacement and radiogenic heat greatly extend duration of the temperature field and the fluid field, provide a favorable conditions for ore-forming. Qianlishan granite pluton are rich in Be, Li, F, Cl and other volatile elements, greatly reduced viscosity and crystallization temperature of the magmatic melt, F could also slow the magmatic crystallization rate and made the magmatic differentiation more fully, so that the mineral elements have a longer time to be extracted, migration, enrichment and mineralization. The heat produced by the radioactive elements also played an important role in prolonged heating time.