Geochemistry of sulfides from massive carbonate replacement type tin ore at Gaofeng, Dachang orefield: Insights into precipitation conditions and enrichment of critical metals

Abstract

Sulfide ore minerals are significant carriers of multiple critical metals, thereby highlighting the importance of evaluating the exploration potential in sulfide-rich deposits. Tin-bearing sulfide ores from the carbonate replacement type tin deposits (cassiterite-sulfide type) generally contain substantial reserves of critical metals as by-products. This study analyzes the major and trace elements compositions of marmatite, arsenopyrite, pyrrhotite, and jamesonite from the Gaofeng deposit using EPMA and LA-ICP-MS. The Gaofeng Sn-polymetallic deposit, situated in the Dachang orefield, the Youjiang Basin, is a typical sulfide-rich carbonate replacement type tin deposit with reserves of 0.23 Mt. Sn, 0.65 Mt. Sb, 1.50 Mt. Zn, 0.79 Mt. Pb, 2800 t Ag and 2000 t In. The No. 100 ore body, hosted within Middle Devonian reef limestone, is intruded by the post-ore granite porphyry dyke. The sulfides account for over 90 wt% of the ore, mainly including marmatite, pyrrhotite, arsenopyrite, and jamesonite. LA-ICP-MS analysis and principal component analysis (PCA) results show that trace element concentrations in sulfides generally exhibit strong spatial consistency and no significant correlation with the horizontal distribution. The spatial uniformity of trace element distribution in sulfides indicates the precipitation rate of each sulfide is relatively high throughout the ore body, and the granite porphyry is closely related to the undiscovered ore-forming granite batholith without a direct role in the ore-forming process. Marmatite is characterized by exploitable enrichment of Cd (5479 ppm) and In (604 ppm), with dominant substitution mechanisms of Zn²⁺ ↔ (Fe²⁺, Mn²⁺, Cd²⁺) and 2Zn²⁺ ↔ In³⁺ + Cu⁺. The Sn content in jamesonite is notably high, ranging from 222 to 4315 ppm (average: 814 ppm), with Sn incorporated via 2Sb³⁺ + Fe²⁺ ↔ 2Sn⁴⁺ + □ and 2Sb³⁺ + □ ↔ Sn⁴⁺ + 2(Ag⁺, Cu⁺). The mineralization temperatures are estimated as 353–372 °C for arsenopyrite, 254–~350 °C for hexagonal pyrrhotite, 329 ± 26 °C for marmatite, and < ~180 °C for monoclinic pyrrhotite, indicating fluid cooling is the key precipitation mechanism for sulfides. The co-precipitation of cassiterite and arsenopyrite is likely controlled by fluid cooling and redox reaction of 3SnCl₂ + 2H₃AsO₃ + 2FeCl₂ + 2H₂S = 3SnO₂ + 2FeAsS +10H⁺ + 10Cl⁻. High mineralization temperature and the “indium window” effect are the dominant controls on indium enrichment in marmatite/sphalerite from carbonate replacement-type tin deposits. Jamesonite shows a tremendous potential for Sn extraction as by-product, where Sn may source from the partial reactivation of the early precipitated cassiterite.