Tin (Sn) Geochemical Mapping Based on a Fixed-Value Method: A Case Illustration in Gejiu Area, Southwest China

Abstract

Geochemical maps play an important role in mineral resource exploration. There are three traditional methods for creating geochemical maps: the cumulative frequency method, the logarithmic interval method, and the Avg±k∗Std (where Avg and Std are the abbreviations of average and standard deviation, and k is a multiple of Std) method. However, with the increasing scope of the study area and cumulative data, the limitations of traditional methods, which depend on the amount of data, are exposed. A fixed-value method for Sn geological mapping is proposed to overcome the limitations of traditional methods. In the fixed-value method, Sn concentrations are divided into 19 levels on 18 fixed values ranging from 1 μg/g (corresponding to the detection limit) to 1000 μg/g (corresponding to the cut-off grade of Sn in hard rocks). The 19 levels are mapped in six color tones. The first to fifth levels are the lowest background areas in blue tones, which correspond to Sn concentrations ranging from the minimum to 3.4 μg/g. The sixth to ninth levels are high background areas in yellow tones corresponding to concentrations less than 10 μg/g, the 10th to 12th are low anomaly areas in pink tones less than 28 μg/g, the 13th to 15th are high anomaly areas in red tones less than 200 μg/g (corresponding to the placer cut-off grade), the 16th to 18th in gray tones less than 1000 μg/g, and the 19th level is in black corresponding to Sn ores with Sn concentration not less than 1000 μg/g. The fixed-value method along with three traditional methods was used to contour the Sn geochemical maps in the Gejiu area in Southwest China. The illustration results of the presented fixed-value method and three traditional methods for geochemical mapping of Sn are all feasible for Sn deposit exploration in the Gejiu area, Southwest China. Compared to traditional methods, the presented fixed-value method overcomes the flaws of traditional methods and is also more meaningful in geochemistry.

Regional Geochemical Characteristics of Lithium in the Mufushan Area, South China

“…To contour the geochemical map objectively, An et al [20] and Xu et al [21] proposed the fixed-value method for Cr and Sn, respectively. According to the construction of the fixed-value method [20,21], a fixed-value method on Li is proposed here on 19 levels according to the method presented by Xu et al [21] and listed in Table 2 along with the values of the fixed-value method on Sn.…”

“…To contour the geochemical map objectively, An et al [20] and Xu et al [21] proposed the fixed-value method for Cr and Sn, respectively. According to the construction of the fixed-value method [20,21], a fixed-value method on Li is proposed here on 19 levels according to the method presented by Xu et al [21] and listed in Table 2 along with the values of the fixed-value method on Sn. In the fixed-value method on Li, to contour the geochemical map, Li concentrations are divided into 19 levels on 18 fixed values which range from 5 µg/g (corresponding to the detection limit) to 1858 µg/g (corresponding to the cut-off grade of Li deposit in hard-rock type).…”

“…The values of lgLi of the total of 3628 records in the Mufushan area are shown in Figure 2a as a histogram, along with its box plot according to the illustration of Xu et al [21]. The box plot is used to show the distribution, focusing on the cumulative frequency, and its typical parameters are listed in Table 1.…”

“…Geochemical maps and geochemical anomaly maps drawn from these data have been basic maps in the geochemical exploration of mineral resources and basic geological surveys [16][17][18][19]. With respect to the geochemical map, a new mapping technique called the fixed-value method was presented and illustrated on Cr and Sn, which can overcome the flaw of dependence on the amount of data [20,21]. The fixed values fully consider the current domestic and international classification, or statistical parameters of element concentrations.…”

“…The fixed values fully consider the current domestic and international classification, or statistical parameters of element concentrations. When a suitable grading value is unavailable, interpolation among adjacent values is used [21]. However, the fixed-value method on Li geochemical mapping has not been proposed.…”