Delineation And Estimation Of Geochemical Anomaly Using Geostatistical Methods

Geostatistical method is a powerful tool for studying the spatial variability of certain things. The variety feature of geochemical element concentration in region could reflect the regional geological processes that control the orientation of geological body and mineral deposits. In this study, the contents of Pt and Pd are analyzed respectively from composite samples. The single sample is recomposed by 64 primary stream sediment samples (1 sample/1km²) mapped at scale 1:20 0000 in eastern Yunnan Province. The dataset of Au,Ag,Cu,Pb,Zn,W,Sn,Mo,As, Sb,B,U,Cr,Ni,Co,V at the same scale is obtained from Yunnan Geomatics Information Center. Firstly, the spatial variety of Pt, Cu and Au is studied using semivariation function; and then factor analysis is used to characterize different types of element associations.The studied results show as follows. (1) The simulated semivariation functions illustrate that the concentrations of Pt, Cu and Au are controlled by the Permian Emeishan basalt of NE trend. The maximal ranges of Pt, Cu and Au of NE trend are 95⁹8km. (2) The results of factor analysis illustrate that the high scores of F1 spatially coincide with the scope of the Permian Emeishan basalt, thus F₁[Cu-Pd-Co-Pt-V-Cr-Ni-Au] characterizes the element association of the Permian Emeishan basalt; Similarly, F2[Sb-As-U-Mo] characterizes that of the Triassic black shale formation; F3[Pb-Ag-Zn-W-Zn-Au-As-Sb-Cu] represents a hydrothermal mineralization association characterizing the Gejiu tin poly-metal deposit, the Dongchuan copper deposit and the Jinping Au deposit. (3) The residual maps created by universal kriging show that the centers of Pt anomaly occurs in the upper Sinian-lower Cambrian black shale formation, Permian thick Emeishan basalt and the contact area of the mentioned above two formations; the centers of Cu anomaly occurs in the Proterozoic black rock series, the Permian thick Emeishan basalt and Gejiu granites; the centers of Au anomaly occurs in the Gejiu granites, alkali intrusions in the south side of Honghe fracture and the basalt and black shale series in southeastern Yunnan. (4) At the scale of 8 × 8km², the centers of Pt anomaly spatiallycoincide with the high scores of factor F1, which may indicate that the basalt is the favorable background for Pt enrichment. Then, within the anomaly scope delineated using Pt data at scale of 8 × 8km², according to one composite sample containing 16 samples covering 4 × 4km², new samples are constructed for analyzing Pt concentration to delineate Pt anomaly at middle scale. Finally, within the anomaly scope delineated using Pt data at scale of 4 × 4km², according to one composite sample containing 4 samples covering 2×2km², new samples are constructed for analyzing Pt concentration to delineate Pt anomaly at small scale. The mentioned above works supply data for analyzing the efficiency of telescope strategy for discovering mineral deposits.(5)The spatial distribution and variety of Pt anomaly at three different scales illustrate the followings: (a) the continuous changing direction of Pt concentration at 3 different scales is NE trend, which follows the distribution of Emeishan basalt; (b) at large scale survey (8 × 8km²), the Pt anomaly is controlled by both SN and NE trends; at middle scale survey (4×4km²), the Pt anomaly is obviously controlled by fractures of both SN and NE trend, therefore most of the centers of Pt anomaly are located at the crossing areas of the mentioned above two trends of fractures; at small scale survey (2 × 2km²), the scope of Pt anomaly is smaller but the anomalous intensity of Pt is stronger than that at large and middle scale survey. There are a Pt anomaly zone of NW trends distributed in the NE corner of this study at small scale survey map, which indicates that there may be a hidden fracture of NW trend affecting the enrichment of Pt. (6) Based on Pt data at three different scale, spatial distribution of Pt anomaly delineated by universal kriging shows that the telescoped Pt anomaly is the best target area of searching for Platinum deposit.