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Baia Mare District - Ilba, Nistru, Sasar, Herja, Baia Sprie, Suior, Cavnic

Romania

Main commodities: Au Ag Pb Zn Cu W
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The epithermal Au-Ag-Pb-Zn-Cu-W ore deposits of the Baia Mare district are located in the Carpathian Mountains of north-western Romania.   Epithermal gold-base metal deposits in the field include, from west to east, Ilba, Nistru, Sasar, Herja, Baia Sprie, Suior and Cavnic which are distributed over a 45 km long WNW-ESE trending interval.   The field has been intermittently mined since Roman times.

The arcuate Carpathian Belt was the product of collision between the African and European plates due to the closure of the Mesozoic Tethyan Ocean. Paleomagnetic data suggest the main subduction event took place in the Late Paleogene to Middle Miocene during which time all of the subducted oceanic crust was consumed. Subsequently, at the end of the Miocene, continent-continent collision began, accompanied by calc-alkaline magmatism and the formation of a large, SW vergent thrust belt composed of Neogene to Quaternary flysch sediments. Calc-alkaline magmatism continued from the Miocene to Quaternary, with the focus of magmatism progressing from NW to SE.

The volcanism and associated mineralisation in the Baia Mare district are closely related to the major sinistral Dragos Voda strike-slip fault system, and to an underlying 65 x 15 km pluton, the boundaries of which define the mineral district. During the Middle and Late Miocene, the Dragos Voda fault system changed to become a normal fault with a down-dropped southern block.

Magmatic activity in the district commenced at ~14 Ma with felsic tuffs and ignimbrites, followed by 13.4 to 9.0 Ma extrusion of basaltic andesites, dacites and andesites followed by the intrusion of small basaltic intrusions at 8.0 to 6.9 Ma (Edelstein et al., 1992, 1993; Pecskay et al., 1994; Kovacs et al., 1997). The dominant andesitic volcanism between 14 and 7 Ma has been divided into three episodes which influenced the pulses of hydrothermal activity. These episodes are bracketed within the:
• Sarmatian Stage (13.5 to 11.5 Ma) pyroxene andesites, which host the Ilba and Nistru vein systems;
• Pannonian Stage (11.5 to 8.5 Ma) dacites and quartz andesites, with the Sasar and Herja veins; and
• Pontian Stage (8.5 to 7.1 Ma) pyroxene andesites with the associated Baia Sprie, Suior and Cavnic ores (Lang, 1979).
These suites of mainly andesitic rocks have a medium K, calc-alkaline association. Petrologic and isotope data suggest a subduction-related and mantle derived magma source with strong crustal contamination (Kovacs, 1998, 1999).

Mineralisation has been dated as occurring during two main episodes, overlapping the three episodes of volcanic activity, namely 11.5 to 10 Ma in the western part of the district at the Ilba, Nistru and Sasar deposits, and from 9.4 to 7.9 Ma in the eastern part at the Herja, Baia Sprie, Suior and Cavnic deposits, between 0.5 and 1.5 Ma after deposition of the respective host rocks (Kouzmanov et al., 2005).

These gold and polymetallic ore deposits have a wide variety of textures, dominantly comprising veins that are cavity filling with bands and druses, breccias and lesser disseminations and stockwork veined structures. The banded veins exhibit a rhythmic deposition with bands that are generally a few millimetres thick, but locally reaching centimetres, comprising alternating metallic ores and gangue minerals. Examples include interlayered quartz-amethyst and base metal sulphides at Ilba and Nistru, and alternatings sulphides, quartz and carbonates in the Cavnic veins, where more than 40 depositional rhythms may been recorded. In the Principal vein at Baia Sprie, the bands (particularly those of sphalerite) reach a thickness of up to 2 m. Spectacular breccia pipes are also found in some deposits (e.g., Baia Sprie, Cavnic, Sasar, Suior), implying phreatomagmatic explosion followed by hydrothermal fluid flow (Milesi et al., 1994; Genna et al., 1994). In deposits such as Cavnic, described below, brecciation is inter-mineral, where pulses of mineralisation are separated by brecciation signifying displacement on the host structures, with the previous pulse occurs as clasts in a matrix of the succeeding stage assemblage (Lang, 1979). At Baia Sprie, breccia textures are an early phase, followed by later banded veins (Kouzmanov et al., 2005). The mineral assemblages within the vein systems include native elements (Au, Ag, Cu, As, S), sulphide minerals (pyrite, chalcopyrite, sphalerite, galena and stibnite), sulphosalts (tetrahedrite, jamesonite, bournonite, semseyite, pyrargyrite) and tungstates (wolframite, scheelite), with quartz, adularia, clay minerals, carbonates, rhodonite and barite as gangue minerals (Grancea et al., 2002).

Hydrothermal alteration of host rocks in the vein selvages is generally irregular. Propylitic alteration is widespread throughout the district and may at least in part by a regional alteration. It consists of andesine, chlorite, epidote and minor calcite, sericite, actinolite and clay minerals (Russo 1971; Stanciu 1973). Where other assemblages are developed, they overprint and separate the vein or structurally controlled breccia zone from the propylitic alteration. The deposits are characterised by the dominance of adularia-sericite alteration fringing silicified zones adjacent to the veins. The adularia-sericite halo grades outwards into an argillic zone. Chlorite is also sometimes found disseminated in the wall rock close to the veins (Russo 1971; Stanciu 1972, 1973; Grancea et al., 2002).

The mineralisation in the field has many of the features typical of low-sulphidation (adularia-sericite) epithermal systems.

At the Baia Sprie deposit, there are two main veins, the steeply dipping, east-west trending Principal and Nou veins, which are 200 to 250 m apart and are parallel to the regional Dragos Voda Fault several km to the south. They occupy fault zones with vertical offsets of several hundred metres, and are found on the margin of an east-west graben filled with volcanic and sedimentary rocks. They are connected by the NE-SW trending Diagonal Fault.   The Principal vein is 5250 m long, up to 22 m wide and it has a vertical extent of over 800 m.   Five main stages of alteration and mineralisation have been recognised in these veins, namely:  i). Fe,  ii). Cu-(Bi)-W, with chloritic alteration,  iii). Pb-Zn, with sericite-argillic alteration,  iv). Sb, and  v). Au-Ag, with an associated adularia-quartz assemblage (Bailly et al., 2002). This mineralisation occurs as early breccias (of the type described in the Cavnic deposit below), followed by late epithermal quartz-sulphide veins

The Cavnic deposit, 10 km east of Baia Sprie, comprises a complex of veins emplaced along NE-SW fractures and subordinate NNE-WSW structures. It produced around half of the total polymetallic metals of the Baia Mare district. In the western and central part of the vein system, the distribution of lodes is controlled by the sub-volcanic roots of a Pontian andesitic volcano. A set of at least 15 significant veins are developed. Each is generally ~0.5 to 1.5 km long and have been mined over a 300 to 600 m vertical interval with thicknesses of 0.5 to 15 m. Mineralisation is interpreted to have taken place as a single phase, composed of three stages of base metal deposition, namely: i). an early predominantly silica-hematite-goethite-magnetite-pyrite-chalcopyrite-colloform silica-chlorite-clay minerals assemblage; ii). an intermediate pyrite-galena-sphalerite-chalcopyrite-tetrahedrite-sulphosalts-quartz-clay suite; and iii). a late pyrite-galena-sphalerite-chalcopyrite-tetrahedrite-rhodochrosite-calcite-quartz-gypsum stage. Breccia structures are typical of this ore and help to define the separation of the three stages. The breccias are indicators of syn-mineral movement on the structures controlling the breccias, in some cases separating the different stages detailed above. Each of the three mineral assemblages was brecciated after deposition, and included as clasts that are cemented by the mineral association of the next (Jude et al., 1970). These breccias are common in all of the Baia Mare deposits, but are best demonstrated at Cavnic, Baia Sprie and Suior.

The Suior veins, 15 km east of Baia Sprie, were among the most recent developed in the district. One of these, the Cremenea vein is 800 m in strike length and persists to a depth of ~1100 m, with widths varying from 2 to 50 m. The deposit is associated with the Cremenea breccia pipe which is on the margin and partially cuts a Pontian pyroxene andesite plug, which in turn cuts Paleogene, Sarmatian and Pannonian sequences. Au-Ag mineralisation predominates in the upper half, where colloform silica is impregnated with gold-bearing pyrite, passing downward to polymetallic ore. The main constituents of the ore are pyrite, wurtzite, sphalerite, arsenopyrite, chalcopyrite, tetrahedrite, galena, boulangerite, marcasite, gold and silver. Gangue comprises quartz, calcite and rhodochrosite. Minor elements are As, Sb, Ga and Mn (Ianovici and Borcos, 1982).

The Nistru field, ~20 km WNW of Baia Sprie, is controlled by the Samartian Piatro Handal volcanic breccia structure. The volcanic structure principally cuts a sequence of Paleogene Tortonian volcano-sedimentary rocks and Samartian pyroxene andesites. Veins are mined over a vertical interval of ~700 m. The veins on the NW side of the field are vertically zoned, with higher Cu at depth, and a number of stages of mineralisation. The earliest Fe-S stage is marked by the sequence hematite, magnetite, pyrite, arsenopyrite, chalcopyrite ±sphalerite with adularia, sericite, chlorite and quartz. The succeeding base metal stage comprises a cupriferous phase (chlorite, ferruginous-silica, hematite, magnetite, pyrite, chalcopyrite with clay minerals) which preceded the lead-zinc sequence (sphalerite, wurtzite, chalcopyrite, galena, pyrite, tetrahedrite, pyrargyrite and marcasite with adularia, chlorite, quartz, clay minerals, barite and calcite). The final stage produced carbonates ± sulphides. The vein system is distributed over a NW-SE elongated ~7 x 4 km area enveloping NE-SW veins that vary from 250 to 1200 m in length and 0.5 to 5 m in thickness (Ianovici and Borcos, 1982).

Remaining resources at the end of 2004 include (Kouzmanov et al., 2005):
    Cavnic - 5.9 Mt @ 2% Zn, 1.5% Pb, 27 g/t Ag, 0.4 g/t Au
            or 20 Mt @ 1 to 3% Zn, 1 to 2% Pb, 1% Cu, 30 gt Ag, 1 g/t Au (Grancea et al., 2002)
    Suior - 9.3 Mt @ 2.3% Zn, 1.4% Pb, 36 g/t Ag, 3 g/t Au
    Baia Sprie - 4.3 Mt @ 1.2% Zn, 1.0% Pb, 0.6% Cu, 29 g/t Ag, 0.4 g/t Au
    Herja - 1 Mt @ 5.2% Zn, 3.5% Pb, 47 g/t Ag, 0.4 g/t Au
    Sasar - 0.15 Mt @ 3.25% Zn, 1.2% Pb, 18 g/t Ag, 1.5 g/t Au
    Nistru - 1.5 Mt @ 1.5% Zn, 0.8% Pb, 28 g/t Ag, 0.6 g/t Au
    Ilba Handal - 0.3 Mt @ 0.6% Cu, 11 g/t Ag, 0.3 g/t Au

For more detail consult the reference(s) listed below.

The most recent source geological information used to prepare this summary was dated: 2004.     Record last updated: 29/3/2018
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.


  References & Additional Information
   Selected References:
Bailly, L., Grancea, L. and Kouzmanov, K.,  2002 - Infrared microthermometry and chemistry of Wolframite from the Baia Sprie epithermal deposit, Romania: in    Econ. Geol.   v.97, pp. 415-423.
Baksheev, I., Damian, F., Damian, G., Prokofiev, V., Bryzgalov, I. and Marushchenko, L.,  2016 - Chemical composition of phlogopite, tourmaline and illite from hydrothermal alterations of the Nistru deposit, baia mare, Romania: in    Carpathian Journal of Earth and Environmental Sciences   v.11, pp. 547-564.
Grancea L, Bailly L, Leroy J, Banks D, Marcoux E, Milesi J P, Cuney M, Andre A S, Istvan D, Fabre C  2002 - Fluid evolution in the Baia Mare epithermal Gold/polymetallic district, Inner Carpathians, Romania: in    Mineralium Deposita   v37 pp 630-647
Ianovici, V and Borcos, M.,  1982 - Romania: in Dunning, F.W., Mykura, W. and Woolley, A.R., 1982 Mineral Deposits of Europe, v. 2: Southeast Europe The Mineralogical Society, The Institution of Mining and Metallurgy, London,    pp. 55-142.
Kouzmanov K, Bailly L, Tamasc C and Ivascanu P  2005 - Epithermal Pb-Zn-Cu(-Au) deposits in the Baia Mare district, Eastern Carpathians, Romania: in    Ore Geology Reviews   v27 pp 48-49
Lang B,  1979 - The base metals-gold hydrothermal ore deposits of Baia Mare, Romania : in    Econ. Geol.   v.74, pp 1336-1351.
Marcoux E, Grancea L, Lupulescu M and Milesi J  2002 - Lead isotope signatures of epithermal and porphyry-type ore deposits from the Romanian Carpathian Mountains: in    Mineralium Deposita   v37 pp 173-184


Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge.   It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published.   While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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