Statistical Analysis of Mercury Data from Soil Survey in Non-volcanic Geothermal System: A Case Study in Sulawesi

Mercury analysis from soil survey is one of the standard methods in geothermal exploration surveys conducted by Center for Survey and Geological Data or PSDG (formerly DIM). The objective of this paper is to analyze thresholds of four non volcanic geothermal systems in Sulawesi, i.e. Suwawa, Marana, Pincara and Mangolo. The value of Hg (ppb) is differ from one prospect to another. Its value ranges from tens ppb up to few thou sands ppb, depends on the geology and geothermal system; in high temperature volcanic geothermal system, or in non-volcanic geothermal system. Therefore determination of threshold that separate background and anomaly is important for better delineation of Hg anomaly area. Prior to threshold determination, a probability plot is used to examine the normality and the existence of sub population within the data. Sub population located at the end left of probability graph or sub population with the lowest range value is assumed containing the background and threshold information. The threshold is then calculated using mean plus one standard deviation of data within this sub population. Comparison of the calculated number with the published threshold value shows very significant difference in term of anomaly area coverage for further exploration target. This paper demonstrates Exploratory Data Analysis (EDA) techniques that can be applied as a tool to determine threshold value. The results suggest that this statistical methodis able to assist and support a better threshold value determination.