0361-0128/01/3238/415-9 $6.00 415 Introduction Several microscopic and microthermometric studies using infrared microscopy have been performed on wolframite, e.g., studies on rocks from Victorio Mountains, New Mexico, and San Cristobal, Peru (Campbell and Robinson-Cook, 1987); Panasqueira, Portugal (Campbell et al., 1988; Lüders, 1996); Erzgebirge, Germany (Lüders, 1996); and St. Michael’s Mount and Cligga Head, England (Campbell and Panter, 1990). These studies were all devoted to W and/or Sn- W deposits spatially associated with granitoid plutons. Wol- framite is an uncommon mineral in epithermal gold deposits, but it has been reported in a number of cases including Baia Sprie, Romania (Ianovici and Borcos, 1982); Cirotan, In- donesia (Milési et al., 1994); El Indio, Chile (Siddeley and Araneda, 1986); Julcani, Peru (Deen et al., 1994), and Crip- ple Creek, Colorado (Bernstein, 1988). The aim of this study is to understand the significance of the presence of wolframite in epithermal-style ore deposits. We focused on Baia Sprie mineral deposit in the Baia Mare district, Romania; it is one of Europe’s major gold-polymetal- lic ore deposits and is rich in tungsten. A combined chemical and microthermometric study using infrared microscopy determined the characteristics of the hydrothermal fluids re- sponsible for wolframite deposition in an epithermal environ- ment and compared these characteristics with those obtained from common epithermal minerals. This paper complements a recent fluid inclusions study of quartz and sphalerite in sev- eral of the Baia Sprie orebodies by Grancea et al. (2002). Geologic Setting and Sample Description Geologic setting The Baia Mare district, located in the northwestern part of Romania, is one of the major metallogenic provinces of the Neogene subduction-related volcanic chain of the Carpathian Mountains (Fig. 1). Miocene calc-alkaline volcanic rocks, which host the ores, were generated in a subduction environ- ment related to the final stages of the closure of the Tethys ocean between Africa and Eurasia (Royden, 1988). The Baia Mare area (Fig. 1) includes some important ep- ithermal gold-polymetallic ore deposits (Ilba, Nistru, Sasar, Herja, Baia Sprie, Suior, Cavnic) and has a long history of mining beginning in Roman times. The volcanism and associ- ated mineralization were closely related to a major strike-slip fault (Dragos Voda) and probably an underlying pluton (Bor- cos and Vlad, 1994; Fig. 1). Mineralization was restricted to SCIENTIFIC COMMUNICATIONS INFRARED MICROTHERMOMETRY AND CHEMISTRY OF WOLFRAMITE FROM THE BAIA SPRIE EPITHERMAL DEPOSIT, ROMANIA LAURENT BAILLY, † BRGM, REM/MESY, 3, Av. Claude Guillemin, BP 6009, Orléans, France LUMINITA GRANCEA, UMR G2R 7566, Université Henri Poincaré, BP 239, 54 506 Vandoeuvre-les-Nancy, France AND KALIN KOUZMANOV ISTO-CNRS, 1A Rue de la Férollerie, 45 071 Orléans Cedex 2, France Abstract The chemical and microthermometric characteristics of wolframite crystals from the Baia Sprie Au-Ag-Pb- Zn-Cu-W ore deposit (Baia Mare district, Romania) have been investigated using electron probe microanaly- sis (EPMA), X-ray elemental mapping, and infrared microscopy. The chemical composition of wolframite changes from a nearly pure huebnerite (MnWO 4 ) core to nearly pure ferberite (FeWO 4 ) rims. This zonation correlates with a decrease in infrared transmittance from core to rims of wolframite crystals as demonstrated by Fourier transform infrared spectra. The Fe content of wolframite may control its infrared transparency, just as the Fe 2+ Mn 2+ substitution controls its transparency in visible light. Microthermometric measurements, performed with an infrared microscope, indicate salinities ranging from 4.6 to 6.4 wt percent NaCl equiv and homogenization temperatures of 154° to 240°C for primary fluid inclusions, all trapped in the Mn-rich zones of the studied crystals. Secondary fluid inclusions showed similar microthermometric characteristics (4.6–6.4 wt % NaCl equiv; temperature of homogenization, 171°–232°C). These microthermometric data agree well with data from previous studies on transparent minerals (quartz, sphalerite) from the Baia Sprie ore deposit. However, it is notable that wolframite appears to have precipitated after scheelite and at lower temperatures. A possible magmatic contribution to ore has been invoked for epithermal gold deposits that contain wolframite, including Baia Sprie. The unexpected low temperatures and low salinities of ore-forming fluids responsible for forming wolframite at Baia Sprie may indicate a mixing of magmatic fluids with a dominant meteoric water component. Economic Geology Vol. 97, 2002, pp. 415–423 † Corresponding author: e-mail, l.bailly@brgm.fr