Studies On Geochemical Characteristics Of Xinshan Area In Kafang, Gejiu

Gejiu in Yunnan province is a famous multi-metal tin-mining area in both China and the world and has a "tin city" reputation. As one of the five ore fields in Gejiu, Kafang mine field attracted widespread attention, and had been engaged in a lot of research work. However, the research materials about Xinshan area in Kafang are very rare. Therefore, doing systemic research in Xinshan area of Kafang for supplementing the additional information in this region is of great significance.This paper employs Kafang Xinshan area as the research object and the modern mineralization theory as guidance, makes use of geological geochemistry, engineering geochemical exploration methods and so forth to study deeply about the geochemical characteristics and primary geochemical anomalies, applies mathematical anomaly for the comprehensive analysis of abnormal primary halo data, and on this basis, combines with the structural characteristics of the area, the situation of alkali metasomatism and the characteristics of granite emplacement to analyses the ore-forming geological conditions in the region and at last predicts the ore-prospecting. In this paper, the main conclusions in the research process are as follows:1. In Xinshan area, polymetallic anomaly is developed, which is large-scale and obvious gradient. The middle element zoning is not significant, and primary anomalies superimposition phenomenon is prevailing, which is important W, Sn, Cu, Mo, and Bi polymetallic ore district.2. The granite of Xinshan area is Yanshan granite, which is part of Laoka rock. The granite in a relatively open area is usually pale and white granite. On a relatively closed condition, granite often forms plaque biotite granite and fine-grained biotite granite. The rare earth elements abundance of granite in Xinshan area is low (ΣREE is often less than 200×10-6); the pattern of rare earth composition is relatively flat, and the distribution curve is "V shaped." Eu anomaly is significant,δEu is generally less than 0.1, and (La/Yb) N ratio is close to 1, or even less than 1.3. Xinshan rock exists the alkali metasomatic alteration of (Na2O+K2O), and the alkali metasomatic alteration and the source of mineralization substance have close relation.4. The wall-rock alteration near rock in Xinshan region can be classified into three types which are the granite inner high-temperature alteration zone, granite outer middle-temperature alteration zone(granite and carbonate rocks exposed alteration zone), and carbonate low-temperature alteration zone according to different wall-rock of rock and mineralization.5. When Xianshan granite emplaced, it pushed up the wall-rock from the bottom to up backwater. However, because the power of wall-rock upward intrusion was less than the static pressure of roof wall-rock, which caused that the granite did not penetrate wall-rock, and it formed an emplacement type of wide and gentle anticline, which was just completely similar with the mode of magma base arch action. But in other conditions, due to the impact of fracture, magma expanded transversely and compressed wall-rock, resulting in the emplacement mechanism of increased magma volume and the balloon expansion model were very similar. From that we can infer that Xianshan granite emplacement mechanism may be a complex emplacement mechanism of a combination with a bottom arch action and the balloon expansion model.6. The mineralization which is related to the granite intrusions stage and hydrothermal after the stage in the area can be divided into the silicate phase, oxide phase, sulfide phase and the carbonate phase in four stages. To clearly identify the four stages of mineralization can provide useful clues for exploration.