A Fluid Inclusion and Critical/Rare Metal Study of Epithermal Quartz-Stibnite Veins Associated with the Gerakario Porphyry Deposit, Northern Greece

Abstract

The Gerakario Cu-Au porphyry deposit in the Kilkis ore district, northern Greece, contains epithermal quartz-stibnite veins on the eastern side of the deposit, which crosscut a two-mica gneiss. Metallic mineralization in these veins consists of stibnite + berthierite + native antimony + pyrite + arsenopyrite, and minor marcasite, pyrrhotite, chalcopyrite, löllingite, and native gold. Bulk geochemical analyses of the ore reveal an enrichment in critical and rare metals, including Ag, Au, Bi, Ce, Co, Ga, La, and Sb. Analysis of stibnite with LA-ICP-MS showed an enrichment in base metals (As, Cu, Pb), as well as weak to moderate contents of critical and rare metals (Ag, Bi, Ce, La, Re, Sm, Th, Ti, Tl). A statistical analysis of the trace elements show a positive correlation for the elemental pairs Ce-La, Ce-Sb, and La-Sb, and a negative correlation for the pair Bi-Sb. Fluid inclusions in the A-type veins of the porphyry-style mineralization show the presence of fluid boiling, resulting in a highly saline aqueous fluid phase (35.7 to 45.6 wt.% NaCl equiv.) and a moderately saline gas phase (14 to 22 wt.% NaCl equiv.) in the system H2O-NaCl-KCl at temperatures varying between 380° and 460 °C and pressures from 100 to 580 bar. Mixing of the moderate saline fluid with meteoric water produced less saline fluids (8 to 10 wt.% NaCl equiv.), which are associated with the epithermal quartz-stibnite vein mineralization. This process took place under hydrostatic pressures ranging from 65 to 116 bar at a depth between 600 and 1000 m, and at temperatures mainly from 280° to 320 °C.

Antimony’s Significance as a Critical Metal: The Global Perspective and the Greek Deposits

“…Older peridotite-serpentinite from the Triassic age, which belongs to the Serbo-Macedonia Massif (Vertiskos unit), are found nearby. According to Stergiou et al [94] the A-type veins found in the porphyry-style mineralization exhibit fluid inclusions that indicate fluid boiling. This process led to the formation of a highly saline aqueous fluid phase (with a concentration of 35.7 to 45.6 wt.% NaCl equivalent) and a moderately saline gas phase (with a concentration of 14 to 22 wt.% NaCl equivalent) within the H 2 O-NaCl-KCl system.…”

“…The Sb-mineralization mostly comprises arsenopyrite, pyrite, berthierite, stibnite, native antimony, and pyrrhotite, with small occurrences of marcasite, chalcopyrite, löllingite, and native gold [94,95]. The occurrence of native Sb indicates that the fluids were supersaturated with respect to antimony.…”

“…The examination of stibnite using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) reveals elevated concentrations of base metals, including Cu and Pb. Additionally, stibnite exhibited relatively notable concentrations to several elements, such as Ag, As, Bi, Ce, Co, Fe, La, Re, Sm, Th, Ti, and Tl [94,95].…”

A Review of the Distribution of Critical and Strategic Mineral Raw Materials in the Vein-Type Mineralizations of Vertiskos Unit, Northern Greece

“…The intrusion-related mineralization includes polymetallic assemblages hosted in quartz veins and/or metamorphic rocks that are enriched in Cu-As-Pb-Bi-Ag-Au-Te or in Sb-W [6,10,11]. Significant polymetallic mineralizations are located across the Vertiskos unit at Laodikino, Koronouda, Stefania-Paliomylos, Kolchiko, Drakontio, and Stanos, while the Sb-W mineralization can be found at Rizana and Philadelphio (Figure 1).…”

“…Table 1. Overview of the typology, alteration, and textural characteristics of the hypogene mineralization hosted in major vein-type deposits found at the Vertiskos unit (data compiled from [5][6][7][8][9][10][11]13,14]). Based on ore assemblages, mineral chemistry, and fluid inclusion studies, two stages of magmatic-hydrothermal activity are mainly documented: an early, higher-temperature stage rich in Fe-As with arsenopyrite-and pyrite-dominated polymetallic massive veins and a later, lower-temperature stage related to the polymetallic quartz veins enriched in Bi-sulfosalts and tellurides.…”