ALKALINE-ULTRABASIC AND CARBONATITE INTRUSIONS OF THE MAIMECHA-KOTUISKAYA PROVINCE, POLAR SIBERIA: MAGMA EVOLUTION AND GENESIS OF Au-Pt-MINERALIZATION

 

Sazonov A.M.*, Zvyagina E.A.*, Gertner I.F.**, Babakhina S.I.*, Krasnova T.S.**,

Vrublevsky V.V.**, Kolmakov Yu.V. **

*Siberian Federal University, Krasnoyarsk, Russia; **Tomsk State University, Tomsk, Russia

sazonov_am@mail.ru

 

The Maimecha-Kotui igneous province in the north of the Siberian craton is known as a large occurrence of Permian-Triassic alkaline-ultrabasic and carbonatite-bearing magmatism in Northern Asia. It is lately considerated this territory perspective for the precious metal deposit prospecting. The variety of petrographic associations presented here is presented by the development of igneous products of several consistent intrusive phases (Egorov, 1991): 1) dunite-olivinite, verlite, clinopyroxenite and there ore variations; 2) melilitolite, uncompagrite, turiarite, okaite and kugdite; 3) jacupirangite, melteigite, ijolite, shonkinite and malignite; 4) nepheline and alkaline syenite, granosyenite and nordmarkite; 5) phoscorite; calcite- and dolomite-bearing carbonatites. The revealed variations of Nd-, Sr-, Pb-isotopic rock composition testify to participation of plume material of PREMA type in the igneous evolution and its displacement with the substance of various crust reservoirs (Kogarko et al., 1999, 2008; Gertner et al., 2009). The designed values of the model age (T_NdDM ~ 0.6-2.4 ba) confirm the heterogeneity of magma-generating substrata.

Substantiation of the spatial and genetic relation of ore mineralization with the derivate of specific phases of the igneous differentiation is a great value for prospecting operations within the province. Decision of this task is complicated with the fact of single discoveries of the precious metal mineralization are known in situ. Some researchers prove the relation of the PGE and gold occurrence with dunites, clinopyroxenites and serpentinites of the Guli intrusion (Malich et al., 1998; Kogarko et al., 1994; Lazarenkov et al., 1993; Dodin, 2000).

There is a belief that several parental magmas could be participated in the establishment of plutons in the Maimecha-Kotui region such as the meimechite (alkaline-komatiite) and alkaline-basaltoid and toleite and the high-calcium (melilitite) ones. Their generation was occurred in various depths and different melting degrees of the mantle matter. According to tests of A.V. Sobolev et al. (1991) showed the parental melt for the forming of cumulative meimechites was probably represent a primitive magma of the alkaline-komatiite type. Their thermodynamic properties are similar to the Archaean analogue, but with higher titanium and alkaline contents. This primary magma was probably formed during the partial melting of the garnet peridotite. It was separated from the mantle restite in depths about 230-300 km at the temperature to 1800-1900 ^оС due to the diapirism of the lower mantle matter. It is established that the composition of melted microinclusions in olivine from meimechite of the Guli volcanopluton indicates their primitive nature (in wt %): SiO₂ 40.81; TiO₂ 2.96; Al₂O₃ 3.92; FeO 12.98; MgO 28.29; CaO 6.98; Na₂O 1.23; K₂O 1.26; P₂O₅ 0.20. Evolution of such magma could evidently lead to formation of ultrabasites and basites of elevated alkalinity in the Maimecha-Kotuiskaya province.

On the other side, results of mineralogical and geochemical studies corresponding to the reconstruction of thermal and baric conditions carried out by I.T. Rass et al. (2000) and L.N. Panina et al. (2001-2009) was testified to the impossibility of the formation of high-calcium melts by the real crystallization fraction of the primary meimechite magma and the autonomy of melilite magma melted out in deep mantle layers. According to modern  data (Panina, 2008; 2009), melt microinclusions in minerals of melilite rocks are compositionally corresponding to the approximate composition of such alkaline ultrabasic magma (in wt %): SiO₂ 36.,5; TiO₂ 12.6; Al₂O₃ 11.1; FeO 6.7; MgO 3.8; CaO 15.0; Na₂O + K₂O 9.2; P₂O₅ 1.5; CO₂ 3.6. At that, it was found the crystallization of perovskite, melilite and monticellite (1280-1160^оС) in hypabyssal magma chambers corresponding to the multiple melt immiscibility of silicate and carbonate liquids. The latter multiplied liquation of within the temperature range of 1200-800-600^оС with formation of alkaline-sulfate, alkaline-phosphate, alkaline-fluoride and alkaline-chloride salt solutions. Usually their mixing is preserved the original composition only in case of quick eruption and hardening mixed.

We have studied new cases for a possible relationship between precious metal formation and polyphase forming alkaline-ultrabasic and carbonatite-bearing magmatism of the Maimecha-Kotuiskaya igneous province (Sazonov et al., 2001). During the study of native gold and iridosmine aggregates from placer deposits within the Guli intrusion territory, it was presented in multiplied inclusions corresponding to mineral parageneses of ultramafites, foidolites, alkaline gabbroids, syenitoids and lack of typical minerals of melilitolite and phoscorite and carbonatite derivatives in them. It was revealed to immediate participation of alkaline-komatiite magmas in the formation of gold- and PGE-bearing mineralization. There are revealed the high content of iridium and osmium in dunites and chromitites as well as ones of platinum and rhodium and ruthenium in serpentinites and magnetite-melilitic rocks. The palladium is more characterized for agpaitic nepheline sienites. Elevated contents of Pt and Au were estublished in dolomite carbonatites.

Within the Krestovskaya alkaline-ultrabasic intrusion located 54 km westward from the Guli volcanopluton, gold and platinum metal minerals in association with sulfides were revealed in melilite- and monticellite-bearing rocks (Sazonov et al., 2001). The following rock associations participate in the geological structure of this massif and its framework: (a) hosting effusive stratified complex of lava flows of melanephelines and their melilite-leicite varieties; (b) the oval in plan plutonic layered body with alternation of olivinites, verlites, pyroxenites, monticellitolites and melilitolites; (C) later dykes presented by alkaline picrites, trachydolerites, alkaline syenite and granosyenite. Industrial gold and platinoid concentrations were revealed in intrusive rocks. Igneous rocks hosting precious metal mineralization consist of olivine, pyroxene, melilite, titanomagnetite and perovskite. Their chemical composition corresponds to “ore” kugdite (mas. %): SiO₂ 26.83; TiO₂ 6.35; Al₂O₃ 1.53; Fe₂O₃ 16.26; FeO 9.68; MnO 0.32; MgO 13.10; CaO 22.10; Na₂O 0.55; K₂O 0.05. Gold and platinum group minerals (ferroplatinum, gold, aurocuprite, iridosmine, rhutheniridosmine) are mainly presented by crypto-grained inclusions and together with associated sulfides (pyrite, pyrrhotite, pentlandite, heazlewoodite, chalcopyrite, djerfisherite, bornite, chalcocite, cinnabar and arsenopyrite) are buried into fine bitumen inclusions regularly distributed in rocks. Most of minerals of the precious-metal complex as well as visually diagnosed particles are presented in the form of metal-organic compounds. Their presence is assumed on the basis of the analytical data of chloroform extracted bitumen from melilite rocks (ppm): Pt 35.3; Pd 24.3; Au 132.4; Ag 176.6; Pb 14348; Cd 4.4; Co 22. An impurity of gold was found in native iron, perovscite, pyrite, chalcosine and rhuteniridosmine. The impurity of PGE was established in galena, titanomagnetite, djerfisherite, magnesian chrommagnetite and pyrrhotite. There are positive geochemical anomalies of precious metals are observed in the fields of development of phenite and melilite rocks. Moreover, single analyses revealed elevated Pd and Au grades in dolomite carbonatites of the Gulinskaya intrusion.

Thus, it is established that the massifs of alkaline-ultrabasic rocks and carbonatites of the Maimecha-Kotuiskaya province are perspective projects for revealing of localized precious-metal mineralization genetically associated with primary (meimechite and high-calcium) magmas and their differentiates.

The studies were supported by the RF Ministry of Education and Science on federal programs of “Development of Higher School Potential (2009-2010)” and “Scientific and Scientific-Educational Personnel of Innovative Russia (2009-2013)”.

 

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