Argillizite “Hats” of Kompleksnoe Ore Occurrence in Kayenmyvaam Volcanic Uplift (Central Chukotka)

Abstract

The article is devoted to the results of mineralogical and geochemical studies of argillizites at Compleksnoe Au–Ag ore occurrence, localized on the southern flank of the Kajenmyvaam volcanic uplift in the inner zone of the Late Cretaceous marginal–continental Okhotsk-Chukchi volcanic belt (OChVB). At the ore occurrence, a series of isometric (oval) in plan view argillizite “hats” with diameters of 200 to 900 m are described. They are composed of red and light gray clay formations and accompanied by complex (Au–Ag–Mo–Cu–Pb–Zn–Bi–Sn) anomalies. In the recent relief, argillizite “hats” are characterized by gently sloping domes and crown subvolcanic bodies of granitoids and explosive breccias. A series of argillizite “hats” is surrounded by elongated lenticular bodies of secondary quartzites, which form the outer boundary of a large annular volcanostructure. The argillizites are composed of the following minerals: illite-smectite (mixed-layered formation), kaolinite, muscovite, jarosite, quartz, and rutile. The average content of Au and Ag in bulk samples are 0.06 and 0.075 g/t, respectively. Au is found in invisible form. According to the geological and geochemical data, argillizite “hats” record a near-surface (up to 300 m), slightly eroded, level of a large porphyry-epithermal mineral-forming system.