Tectonic Position of the Alshar Au–As–Sb–Tl Deposit, Macedonia

During the second half of the 20th century, several dozen large and medium deposits of disseminated pyrite–marcasite ores with total gold reserves of more than 6000 t and annual gold production of ~200 t were found in the Basin and Range Province, Nevada, United States [1, 2]. This unique gold district is termed as the Carlin trend. The limited development of the Carlintype mineralization in other gold districts of the world is presently a debated issue. Naturally, each Carlin-type mineralization inferred beyond Nevada requires detailed investigations. In 2004, we began to study the Alshar deposit with Carlin-type mineralization together with Macedonian geologists [3]. The Alshar deposit is a large object in terms of Tl reserves and a medium reserve in terms of inferred Au reserves [3, 4]

Multilevel Structure of Ore-Magmatic Columns in Large Ore Deposits

Mining of large deposits and prospecting for separate ore occurrences at deep levels has provided new data on the deep structure of ore-magmatic columns and variation in the mineralization types replacing each other with depth [1]. For example, veinlet-disseminated ores of the porphyry type are localized at relatively deep levels of copper, molybdenum, tin, tungsten, and gold deposits. At a hypsometrically higher level, they are replaced by ores of the vein type. Simultaneously, the type of deposits also changes toward quartz and polysulfide ones. Vein ores represent differentiates of porphyry mineralization matter

Formation Conditions of Copper Porphyry Mineralization in the Kadica–Bukovik Ore District, Eastern Macedonia

Macedonia is located in the Serbian–Macedonian sector of the Eurasian Tethys metallogenic belt (Fig. 1). Mineralization related to Cenozoic activation in this area is expressed in the formation of a volcanoplutonic complex in the dispersed spreading setting [1]. Previous joint works with Macedonian geologists made it possible to establish that the present-day tectonic structure of Macedonia reflects dislocations closely related to Cenozoic magmatism and productive mineralization [2]. The Kadica–Bukovik ore district is located in the easternmost Surdulica–Osogovo–Pasos metallogenic zone characterized by the wide development of lead– zinc mineralization (Fig. 1). The zone incorporates systems of sheeted bodies and discordant dikes of quartz latites with an absolute age within 24–12 Ma. Recent discovery of the gold-bearing porphyry copper mineralization in the eastern Kadica ore district is inconsistent with its metallogenic specialization and previous metallogenic model of this belt [2]. To study this phenomenon, we carried out complex studies, which involved structural–geomorphological analysis of ore district [4], on the one hand, and thermobarogeochemical study of ore formation conditions, on the other hand

The Alshar Epithermal Au-As-Sb-Tl Deposit, Southern Macedonia

The results of tectono-metallogenic, geological-structural, mineralogical, isotopic and thermobarogeochemical studies at the Alshar deposit and in the adjacent area are discussed. The data obtained show that the gold mineralization at the deposit is similar to that observed at the Carlin-type deposits in the western United Stales. Similar characteristics include the Au-As-Sb—Tl-Hg geochemical assemblage; low Pb, Zn, Cu, and Ag contents in ore; widespread jasperoid and argillic metasomatic alterations of host siliciclastic-carbonate sedimentary rocks; and the spatial relations to fault zones. At the same time, the Alshar deposit differs from the Carlin-type deposits by the following features: (1) Pliocene age of mineralization. (2) expansion of mineralization over younger volcanics, (3) a high Tl grade in ore, and (4) localization of the ore field in a long-lived central-type magmatic structure. The results obtained can be used as an exploration model