Toward a mineral potential map of central Aceh, North Sumatra: contributions from spectrum-area and local singularity fractal analysis of stream sediment geochemistry and its relationships to magmatic-hydrothermal Cu and Au mineralisation

Abstract

A reassessment of the geochemistry of stream sediments collected by the British-led North Sumatra Project from 1975 to 1980 in central Aceh with spectrum-area and local singularity fractal techniques refines previously determined areas with anomalous Cu and delineates As anomalies (proxy for Au) that correspond to porphyry Cu and epithermal Au-Ag deposits and prospects discovered in the 1980s and 1990s. Additionally, the application of these methods to stream sediment samples collected by an Australian company in the mid-1990s from part of central Aceh identifies Au, As, and Cu anomalies that are aligned with regional geochemical trends. Integrating singularity metal-enriched areas and the distribution of mineral occurrences and structures reveals northerly and easterly tectono-magmatic corridors controlling epithermal Au-Ag and porphyry Cu mineralisation. The above results attest to the usefulness of legacy data for first-pass mineral assessments and for providing evidence layers for a future mineral prospectivity map.

Porphyry and skarn Cu prospectivity of Sumatra with GIS spatial modelling techniques

“…Ref. 22 ). This remark applies to the enriched singularity spots in the Barisan foothills and coastal areas.…”

“…An example of the latter, labelled A1, is located in the Tripa concession, where it positively correlates with the recently mapped intrusions and metalliferous stream sediments. 22 However, most of the additional favourable areas lie along the SFS or its splays, where the fault-controlled stream sediments are rich in Cu and the associated metals, which are interpreted to be signal noise. We interpret this 'false' anomaly as being due to the so-called over-fitting issue in MPM (e.g.…”

“…Ref. 22 ), and hence the NW and N trending buffered structures were combined with the fuzzy OR operator into an intermediate buffered structural map (Figure 7(b)). By contrast, the fuzzified structural map of the CS Sumatra segment is based on the NW-trending structures (Figure 8(b)).…”

“…To our knowledge, there are no quantitatively integrated Cu potential maps for Sumatra available in the public domain. Instead, Page and Young 21 defined Cu and Pb anomalous areas in north Sumatra from 4°N to 5.65°N on the basis of a basic statistical analysis of the stream sediment compositions, and Mulja 22 produced multi-metal-enriched localities in central Aceh between 3.75°N and 5.1°N by using the spectrum area and local singularity fractal techniques on the same sample medium. Thus, devising new porphyry and skarn Cu prospectivity maps of Sumatra with geographical information system (GIS)-based approaches is warranted in order to identify new potential exploration areas.…”

Editorial

“…This issue contains papers focused on a range of different aspects of mineral exploration, the distribution of metals within mineralizing systems, and the processes involved in the formation of mineral deposits. The first of these papers is by Mulja (2022) who focuses on stream sediment geochemical data for the central Aceh area of northern Sumatra, Indonesia, as part of efforts to generate mineral potential maps for this region for hydrothermal Cu–Au mineralisation. The paper by de Oliveira et al (2022) focuses on the 3D distribution of Cu, Zn, and Pb within the Palmeirópolis volcanogenic massive sulphide (VMS) deposit, located in Tocantins state, central Brazil.…”