PETROMETALLOGENIC UNITS RELATED TO MAGMATIC DOMAIN-DISTINGUISHING CRITERIA

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1 PETROMETALLOGENIC UNITS RELATED TO MAGMATIC DOMAIN-DISTINGUISHING CRITERIA MARZA 1 Ioan, KOVACS 2 Marinel 1 Babes Bolyai University, 3400 Cluj Napoca, 11, Avram Iancu str., ioanmarza@personal.ro 2 North University Baia Mare, 4800 Baia Mare, 62/A, Victor Babes str., marinelkovacs@yahoo.com 1. Introduction.The lack of a single and unanimously accepted opinion regarding the systematics of metallogenic-petrometallogenic units and their identification led in time to regretable inconsistences. Initially, the metallogenic units and subunits based on economic criteria and on the spatial (geographical) distribution of ores have been taken into account. Later on, new criteria based on geological elements have been involved (according to Launay, de L., 1913; Emmons, 1913; Lindgren, 1933; Bateman, 1956; Petraschek, 1965 and many others). The introduction of the petrometallogenic concept in the study of ore deposits (Abdullaev, 1954; Mârza, 1990, 1995, 1999) has represented an important moment in understanding the genesis of the ores, specially based on global tectonics. In his papers, Mârza promotes a new view on the petrogen-metallogen concepts, based on an inseparable process developed in all the geological environments (magmatic, metamorphic, exogeneous). Considering the magmatic metallogenesis as inseparable from petrogenesis, it is rather more correct to take into account the petrometallogenic units and subunits than the metallogenic ones. The paper approaches the criteria necessary in distinguishing the petrometallogenic units and subunits from the magmatic field, specially those from the mobile areas (rift and subduction). These units and subunits are briefly characterized as well, with examples from Romania. 2. Distinguishing criteria of the petrometallogenic units. In order to define criteria to distinguish the petrometallogenic units it is difficult to identify the stages of the evolution of the spatial units (provinces) and their correlation with petrometallogenic epochs (as geochronologic, temporal sequences). The specificity of the time and space evolution of magmatogenic geostructures (mobile and anorogene), expressed by its products-rocks and mineralizations-different as amount and quality, determines the split of units into metallogenic-petrometallogenic subunits. Some of the resulted criteria are as follows in the systematics of petrometallogenic units. a. The geostructure (type of geostructure) represents the tectostructural element, the basic criterium in petrometallogenic systematics. Based on this criterium, the major petrometallogenic units, the petrometallogenic belts and provinces respectively, may be defined. 135

2 b. The stages/substages of the temporal and spatial evolution of the geostructures form another criterium in order to identifying petrometallogenic subunits. c. The homogeneous petrogene-metallogene character of the geostructural units and subunits in a certain stage of temporal and spatial evolution. Based on this criterium, magmatic petrotypes, metallogenic phases, types of mineralizations (veins, metasomatic bodies, endogeneous breccias, etc), geochemical systems (LS and HS), geochemical associations (major and minor elements), mineral paragenesis, ore structures and textures, metal sources and thermobaric regime have been defined. The petrogene and metallogene indices of a specific area facilitate the assessement and the identification of the petrometallogene units. Multiphase products from a structural unit/subunit disturb this process of understanding but identifying the magmatic evolution and the cogenetic metallogenesis is the best way leading to a correct interpretation. d. Comparative criterium (resulted from the above mentioned) consists of a permanent comparative analysis of petrogene-metallogene parameters of the investigated structures, outlining isopetrometallogene surfaces with different positions within the geostructures. e. The spatial criterium (area of development) is an undeterminant factor which sometimes needs to be taken into account. 3. Petrometallogenic units related to the magmatic domain from mobile zones.the magmatic field from mobile areas consists of a typical gradational succession of petrometallogene units: belts, provinces, subprovinces, districts, fields, ore deposits and ore bodies as follows. The petrometallogenic belts correspond to the largest structural-petrometallogenic (magmatogenic) units, superimposed over the limits of the plates in different stages of evolution. They are liniar structures with compressive character (subduction zones, eg. the Alpine-Carpathian structure) or expansive character (rifts, eg. East-African Rift). Petrometallogenesis is correlated with the type of geostructure, generating predominantly intermediary magmatites in subduction areas (with complex and gold-silver mineralizations) and basic magmatites in rift areas (with Cr, Fe, Ti, etc. orthomagmatic mineralizations and volcanogenic-sedimentary ones). The petrometallogenic provinces are units subordinated to belts, more or less incorporated into belts. They correspond to continental and subcontinental megastructures ( frequently up to 1000 km size) and consist of a relative homogeneous (monocyclic, rarely expressed) and heterogeneous (polycyclic, frequently expressed) petrometallogenesis. The mobile megastructures (subductive, riftogene) corresponding to provinces may develop into a relative short period of geological time, having a less differentiated petrometallogenesis or may develop in a succession of 136

3 stages covering a longer time interval and leading to segments of different petrometallogenesis, outlining subprovinces, districts, etc. The province represents the basic unit in petrometallogene systematics, independent of the endogeneous or exogeneous field; the magmatogene provinces or the tectostructural frame is tightly correlated with the petrogenic-metallogenic epochs. The petrometallogene provinces are spatial geostructural units with a structogene evolution, specific magmatism and metallogeny. The petrometallogene epochs are geochronologic sequences of petrometallogene evolution. The petrometallogenetic subprovinces are subordinate units, counterparts of provinces with specific features not necessarily outlined as separated in the systematics. The petrometallogenic districts correspond to mezostructures (regional structures) which are subordinated to provinces/subprovinces or may form independent structures developed on areas not more than 100 km. Districts have homogeneous characters in most of the cases (eg. Brad- Sacaramb, Stanija-Zlatna, etc., Au-Ag +/- Te, veins and breccia pipe structures), with differences own to polycyclicity or stage evolution (eg. Oas, Baia Mare districts with complex-pb, Zn, Cu and Au-Ag). The petrometallogenic fields are districtual subunits (not more than tens of kilometers size, around 30 km the most well developed ones); they may be identified within some of the districts, based on specific characters or may be isolated, without any connections with the districts, with a monocyclic petrometallogeny (eg. Rodna petrometallogenic field with base metal mineralizations associated to Neogene magmatic rocks). The ore deposits, composed of several or a single ore body (eg. porphyry copper structures, Fe, Cr, Ti orthomagmatic stratabound bodies), are locally developed, reflecting the general features of a major geostructure they belong to. Their sizes differ very much, from very large to very small ore deposits (Laznicka, 1999; Marza, 1999). The hydrothermal ore deposits associated to the Neogene magmatism from Baia Mare region may be considered as belonging to well outlined petrometallogenic units and subunits in accordance with the above mentioned criteria. These units may be defined as follows: The Tertiary petrometallogenic province of the Carpathians, as a major unit corresponding to the geostructures represented by the subduction area from the European Plate margin. Calc-alkaline magmatic rocks related to the Miocene subduction are associated with typical Au-Ag and base metal epithermal and subordinate porphyry copper mineralizations. The petrometallogenic subunit including Baia Mare ore deposits may be defined as the Eastern Carpathians Neogene petrometallogenic subprovince corresponding to the Neogene volcanic chain and associated mineralizations represented by Slansky-Vihorlat-Gutai-Beregovo- Oas-Gutai-Calimani-Gurghiu-Harghita Mts. Magmatic rocks are predominat andesites belonging to 137

4 the intermediate arc-type volcanism with typical epithermal mineralizations (less in Calimani- Gurghiu-Harghita Mts.). The Neogene petrometallogenic subprovince of the Eastern Carpathians consists of several districts among which Beregovo-Oas (Turt) and Baia Mare are including the epithermal ore deposits from Oas Mts. and Gutai Mts., respectively. Beregovo-Oas petrometallogenic district includes the Neogene magmatic rocks from Transcarpatia (Gutin Range and Beregovo) and Oas Mts. with similar volcanological and petrological features. Most of the volcanic structures are represented by extrusive domes of acide and intermediate composition (Kovacs, Fulop, 2002). Mineralizations are epithermal base metal + Au-Ag and some of them Hg as well. Baia Mare petrometallogenic district includes the Neogene magmatites and associated epithermal mineralizations from Gutai Mts. The mineralizations consist of typical low-sulfidation, related intrusions, predominant vein-hosted polymetallic and gold-rich epithermal deposits (Kovacs, 2001). The hydrothermal alterations are predominant adularia-sericite type. The spatial distribution of the ore deposits within Baia Mare district is determined by the structural/tectonic control of the Carlibaba-Carei (Dragos Voda/Bogdan Voda) transcrustal fault from the southern part of Gutai Mts. Three petrometallogenic fields may be outlined as subunits of the Baia Mare district, with spatial distribution and distinctive features: Ilba-Nistru, Sasar-Dealul Crucii, Herja-Baiut. Sasar- Dealul Crucii petrometallogenic field represents a typical low-sulfidation gold epithermal system and Ilba-Nistru and Herja-Baiut fields include low-sulfidation base metal+/- gold, copper epithermal deposits. The ore deposits, as subunits of the petrometallogenic fields, have generally been identified based on their distinctive peculiarities. Each one of them may be more or less consistent with the types of epithermal ore deposits defined by Leach and Corbett (1996). Sasar ore deposit is therefore a typical quartz, gold silver low-sulfidation epithermal deposit and Cavnic ore deposit represents a typical carbonate base-metal gold related intrusions epithermal deposit. 138

5 References: Abdullaev, H.M. (1954). Legătura genetică a mineralizaţiilor cu intruziunile genetice. Ed. Tehn. şi Şt., Moscova, 314 p. (translated from Russian) Bateman, A.M. (1956). The formation of Mineral Deposits. John Wiley &Sons, Inc., New York. Emmons, S.F. (1913). Ore Deposits. Am. Inst. Min., 5 Eng., New York. Kovacs, M. (2001) - Subduction - related magmatism and associated metallogeny in Baia Mare Region (Romania). Rom. J. Mineral Deposits, Vol. 79, Suppl. 2, p. 3-9, Bucharest. Kovacs, M., Fulop, A. (2002). Neogene volcanism in Oas Mts., Eastern Carpathians, Romania, Geologica Carpathica, vol 53, p Bratislava Launay, de L. (1913). Traite de Metallogenie. Gites mineraux et metallifere. Ed. Ch. Beranger, Paris Laznicka, P. (1999). Quantitative relationships among giant deposits of metals. Econ. Geol., 94, 4, Leach, T.M., Corbett, G.J. (1996). Characteristics of low-sulfidation gold-copper systems in the south-west Pacific. In South-West Pacific Rim gold-copper systems: structure, alteration and mineralization. Pacrim Conference Workshop, 1995, 185 p. Lindgren, W. (1933). Mineral deposits (Fourth Edit.). McGraw-Hill Book Comp., Inc. New York and London, 930 p. Mârza, I. (1982). Geneza zăcămintelor de origine magmatică. Vol. I, Edit. Dacia, 250 p., Cluj Napoca Mârza, I. (1990). Petrometallogeny-fundamental concept in geology. Rev. Roum. Geol.-Geophys.- Geogr. (Ser. Geol.), 34, 35-39, Bucuresti Mârza, I. (1995 a). Petrometallogenetic concept, theoretical and applied significance. Studia Univ. Babes-Bolyai, Geologia, 1, 73-83, Cluj Napoca. Mârza, I. (1995 b). Tentative d elaboration de la terminologie des petrometallites. Studia Univ. Babes-Bolyai, geologia, XL, 1, , Cluj Napoca. Mârza, I. (1999). Geneza zăcămintelor de origine magmatică. Vol. 4, Presa Universitară Clujeană, 486 p., Cluj Napoca. Petraschek, W.E. (1965). Typical Features of Metallogenic Provinces. Econ. Geol., 60, 8,

1. Geological setting

1. Geological setting NEOGENE VOLCANISM IN OAS MTS., EASTERN CARPATHIANS, ROMANIA M. KOVACS and A. FULOP North University, 62A, V. Babes street, 4800 Baia Mare, Romania Abstract: Oas Mts., the northernmost part of Neogene volcanic