Semi-detailed geochemical survey for chromium, Nickel, Cobalt and copper in the ultramafic terrain and vicinity, amphoe Wang Nam Yen , changwat Prachin Buri

Abstract

Geochemical investigation has been carried out in the ultramafic terrain and its vicinity at Amphoe Wang Nam yen, Changwat Prachin Buri. The study area covers approximately 250 square kilometres. A total number of 327 stream sediment samples were collected from accessible tributaries at a sampling interval of 150-200 metres along the stream, and 654 B-horizon soil samples were also taken from stream banks. All samples have been determined for Cr, Ni, Co and Cu by atomic absorption spectrophotometric method. The overall frequency distribution of each element was treated statistically. Probability graphical method was employed for the selection of threshold values. The geochemical maps were produced by using the ranges which limited by appropriate cumulative percentile levels. The Cr anomalous zone situates within the serpentinized rocks and relates to chromite mineralization. The strong Ni and Co anomalies are also located and relate to the ultramafic terrain. A number of small Cu anomalies with no obvious lithologic association are scattered throughout the sampled area. A moving average method was applied to separate various components of geochemical landscape by using different cell sizes and finally, the residual maps were obtained. Trend surface analysis was a procedure whereby the background or regional components are separated from random local variations by mathematical process. Microcomputer was used to compute and construct the polynomial trend surface and residual maps. The geochemical surfaces obtained from moving average method and trend surface analysis are coincident with the anomalous patterns produced by probability graph presentations. The cluster of significant Cr, Ni and Co anomalies underlain by ultramafic terrain covering an area of approximately 2 square kilometres are considered to be top priority for further detailed investigation.