Abstract
The Maikain deposit is situated 130 km to the south-west from Pavlodar city in north-eastern Kazakhstan. It is located within the late Riphean – early Paleozoic Maikain anticline. It comprises 12 mineralised sites, 6 of which are of economic significance as follows: Maykain A, B, C, D, F and the New Vein. The Maikain B is the most typical and best studied deposit, and it is the subject of this study. The Maikain deposit is one of few examples of lower Paleozoic volcanogenic massive sulphide (VMS) deposits of gold, silver, copper, zinc and lead. The early to middle Ordovician Maikain deposit exhibits characteristics of a transitional type between the Uralian and Rudny Altai types (Yakovlev 1998; Lobanov et al. 2014), or bimodal-mafic type (Barrie & Hannington 1999). The Maikain ore district is located within the Maikain metallogenic zone, representing the ensimatic island arc of the later stage that formed on the oceanic crust during the Ordovician. The Maikain ore district is located within the field of the Bozshakol spilite-keratophyre formation. Volcanic rocks are divided into two sub-formations: the Lower, Dzhangabul formation, composed of intermediate volcanics, and the Upper, Aschikol formation, consisting of acid lavas and pyroclastics alternating with marine clastic sediments. The ore field is confined to the transitional horizon between the Dzhangabul spilite and the Aschikol keratophyre subformations, cross-cut by plagiogranite porphyry dikes.
The Maikain ore field is located within a large fault zone of the Salair orogeny resulting in host rocks being fragmented into smaller blocks. Volcanic rocks of the Bozshakol formation are strongly altered and transformed into silicified (‘secondary quartzites’), quartz-sericite, chlorite and quartz-chlorite schists. Maikain ore field is located in the eastern wing of the third-order anticline in the eastern part of the late Riphean – early Paleozoic Maikain synclinorium. The ore field represents a volcano-tectonic depression similar to cauldron subsidence (Kaipov & Taranto 1974; Yakovlev 1998). The Maikain B deposit is composed of lower-middle Cambrian sedimentary-volcanogenic rocks. All ore bodies are localised within a large foliated zone. Mineralised zone comprises series of lenses occurring concordantly with host rocks. The main four ore bodies are composed of massive ores, have clear contacts and pinch-out gradually. Three main ore types are distinguished and listed here in order of their formation: massive; massive-barite-polymetallic and barite-polymetallic. Each type is characterised by specific mineral associations (Yarenskaya 1971). Au and Ag content increase from one ore type to the next; also, Cu, Pb and Zn grades in two latter ore types are similar and significantly higher than in the massive ores. The deposit was formed near-surface (at sub-volcanic level). Pre-ore metasomatites were formed at 510–420°C and economic mineral associations – at 490–340°C by way of intrusion and recrystallisation of highly-concentrated sulphide fluids of fluid-melt or mineralised magma types (Parilov 2012).