Geological, geophysical, and geochemical characteristics of the Ban Kiouchep Cu–Pb–Ag deposit and its exploration significance in Northern Laos

Abstract

The Simao–Indochina Basin is located between the Loei–Luang Prabang–Dien Bien Phu fold belt and the Jinghong–Nan-Uttaradit suture zone, composed of Mesozoic and Cenozoic red beds. It overlies the marine clastic rocks and volcanic sedimentary rocks of a Paleozoic back-arc foreland sequence. The Late Triassic Indosinian orogeny and subsequent superimposition and intracontinental shearing and structural superimposition may have facilitated the formation of various deposits in this basin, including hydrothermal, skarn, and porphyry types of mineralization. The Ban Kiouchep Cu–Pb–Ag deposit is a medium–low-temperature hydrothermal deposit that is largely controlled by faults and is hosted in carbonate rocks and volcanic (-sedimentary) rocks. The formation of this deposit includes a series of geological and metallogenic processes (i) neritic–littoral facies (volcanic-) sedimentation in a Late Paleozoic to Late Triassic back-arc foreland setting, (ii) Indosinian orogenic transformation, (iii) Mesozoic–Cenozoic tectonic-hydrothermal overprinting, and (iv) epigenetic oxidized leaching. The ore minerals are primarily malachite, azurite, and galena, followed by sphalerite, chalcocite, and chalcopyrite, with associated silver minerals. Using induced polarization (IP) geophysical surveys and soil geochemical surveys, large-scale and highly overlapping coincident anomalies and a mineralized zone at a scale of 100–110-m size (ore body I) was discovered in the area. Two anomalies, P1-C1 and P5-C4, with the best metallogenic conditions and the deepest extensions of the known ore bodies, were further selected as engineering verification targets. The two following verifying drill holes revealed Pb–Zn–Ag mineralization in the fault zone; however, no mineralized ore bodies consistent with the anomalies were found. The high background value of the Fe–Cu–Pb–Zn (Ag) elements, strong fracturing, and hydrothermal alteration, as well as later oxidized leaching with lateritization, resulted in in-situ dispersion and local secondary enrichment of the metallogenic elements. These may be the primary causes of the overlapping anomaly distribution along the strata and faults therein. Lateritic Ag mineralization has been also found in the area. The geological, geophysical, and geochemical characteristics and the prospecting are of great importance for further research and prospecting for other related deposits, for example, the VHMS, SEDEX, hydrothermal Cu polymetallic deposits and porphyry, skarn, epithermal, sediment-hosted/orogenic Au deposits, with lateritic Ag (Au) deposits in the Simao–Indochina Basin of Northern Laos.