Intense chemical weathering in tropical environments poses challenges for conventional geochemical exploration, as primary lithological signatures become heavily altered. Stream sediment geochemistry provides a robust alternative for detecting anomalous geochemical patterns under these conditions. In this study, 636 stream sediment samples and 15 rock samples were evaluated using Principal Component Analysis (PCA), Median + 2 Median Absolute Deviation (MAD), and Concentration–Area (C–A) fractal modeling to identify potential anomaly zones. These results were compared with the traditional Mean plus 2 Standard Deviation (SD) approach. The findings indicated that Mean + 2SD offers a conservative threshold but overlooks anomalies in heterogeneous datasets, while Median + 2MAD provides robustness against outliers. The C-A fractal model effectively characterizes low- and high-order anomalies by capturing multiscale variability. Elements such as Au–Ag–Hg–Se–Sb–As form a system indicating low- to intermediate-sulphated epithermal mineralization. Au–Pb points to polymetallic hydrothermal mineralization along intrusive contacts. The southern region is a primary mineralization center controlled by an intrusive–volcanic boundary, whereas the east and west areas exhibit secondary mineralization, characterized by altered lava breccia. The correlation between shallow epithermal and deeper intrusive-related porphyry systems, especially regarding Au–Ag, offers new insights into the metallogenic landscape of the Sunda–Banda arc. Beyond regional significance, this research presents a geostatistical workflow designed to mitigate exploration uncertainty in geochemically complex zones, providing a structured approach applicable to volcanic-arc mineralized provinces worldwide.

This research was conducted to identify the characteristics of laterite deposits in the western and eastern blocks of Sebuku Island, Kotabaru Regency, South Kalimantan using field observation methods, and laboratory analysis including titration, XRF, XRD and petrography analysis. The characteristics of the western block laterite deposits are 10 meters until 15 meters deep. The red limonite zone has Fe content of 51.25% with a mineral composition of hematite, magnetite, goethite, ilmenite, spinel. The yellow limonite zone has Fe content of 50.1% with a mineral composition of goethite, hematite, gibsite, ilmenite. The saprolite zone has Fe content of 16.2%, the mineral composition is hematite, chrysotile, goethite, garnet, diopside. The characteristics of the eastern block laterite deposits are that they have a depth of 6 meters until 7.5 meters. The red limonite zone has Fe content of 47.38% with a mineral composition of hematite, goethite, ilmenite, spinel. The yellow limonite zone has Fe content of 38.70% with a mineral composition of goethite, hematite, chromite, gibbsite, spinel. The saprolite zone has Fe content of 15.08%, the mineral composition is hematite, goethite, diopside, fayalite. The bedrock of the research area is in the form of periodotite, namely dunite and harzburgite which have been serpentinized. The mineral composition of the bedrock is olivine, pyroxene, opaque minerals and several secondary minerals, namely serpentine and talc. The west block bedrock has Fe content of around 7.73 % until 8.03% while the east block bedrock has Fe content of around 6.59 % until 7.49%.