(Pb–Sb)-bearing sphalerite from the Čumavići polymetallic ore deposit, Podrinje Metallogenic District, East Bosnia and Herzegovina

Abstract

Čumavići is a medium– to low–temperature hydrothermal Sb–Zn–Pb–Ag polymetallic vein–type ore deposit in the Srebrenica orefield, part of the Podrinje Metallogenic District, Eastern Bosnia and Herzegovina. The ore deposit occurs in the form of simple and complex veins along faults and fractures, as well as stockworks and disseminations hosted within Neogene volcanic rocks (pyroclastics and andesite lavas of calc–alkaline affinity). The deposit comprises sulfides (sphalerite, galena, stibnite, pyrite, marcasite, chalcopyrite, arsenopyrite, gudmundite, safflorite, löllingite, gersdorffite and acanthite), sulfosalts (berthierite, geocronite, boulangerite, semseyite, plagionite, jamesonite, bournonite, twinnite, andorite, fizéliyte, Ag–bearing tetrahedrite, stephanite, polybasite, pyrargyrite and argyrodite), native gold and silver, tungstates (hübnerite), oxides, and gangue quartz, chalcedony, Mn–siderite, anglesite, smithsonite, fluorite, gypsum and ludlamite. Three generations of sphalerite are recognized in the Čumavići deposit, evolving from Fe–rich to Fe–poor. The most common are yellowish to colorless Fe–poor varieties. Electron Probe Microanalyses of sphalerite free of micro–inclusions of galena and Pb–Sb-sulfosalts revealed wide compositional variations in minor- and trace–element contents (e.g., Fe, Cd, Mn, Cu, Sn, As, and In). Of particular interest are the lead and antimony content of sphalerite, which vary from 0.10 to 3.08, and 0.02 to 1.62 wt.%, respectively. Lead– and Pb–Sb-rich zones are the most common in sphalerite, while individual Sb–bearing zones are rare. These zones have fan–like forms with circular to wave-like, micron–scale bands, filled with galena or Pb–Sb sulfosalts. In the Pb–Sb zones, the Sb/Pb atomic ratio ranges between 0.3 and 1.5, similar to ratios between geocronite and jamesonite, thus suggesting the presence of micro– to nano–scale inclusion of sulfosalts within the sphalerite. The mean composition of all sphalerite samples is (Zn0.78–0.99,Fe< 0.01–0.21,Cu0.00–0.02,Pb< 0.01–0.01,Cd< 0.01–0.01,Sb< 0.01–0.01,Mn< 0.01–0.01)∑ 0.97–1.03S0.97–1.08 (Sn and As atomic proportions are < 0.01 apfu). In all sphalerite samples, excellent negative correlations have been determined between Fe and Zn, and ∑(Fe + Sb) and Zn. The studied mineralization shares many mineralogical and geological characteristics in common to polymetallic Sn–Ag–Sb deposits in Bolivia and elsewhere.