Abstract

Valentinite forms through the alteration of stibnite in sulphide deposits. Colloform sphalerite is a widespread mineral in low-temperature deposits, particularly those of the Mississippi-Valley type. We identified valentinite and colloform sphalerite in hydrothermal deposits occurring in the Baia Mare area. The Baia Mare metallogenic district of Neogene age occurs in the northwestern part of the Neogene volcanic chain within the Eastern Carpathians. The Neogene volcanism from Baia Mare area is related to the subduction processes of the East European plate under two microplates, Alcapa and Tisza-Dacia/Tisia, in the post-collisional compressive phase. We have identified valentinite in the Dealul Crucii and Baia Sprie deposits, associated with other epithermal minerals, in the absence of the stibnite. Valentinite is deposited in the final phase of the epithermal process after calcite and manganese-bearing calcite. Micro-Raman and microprobe determinations indicate the presence of valentinite. The formula of valentinite is close to stoichiometric Me2O3 and contains small amounts of tin as an antimony substituent. Colloform sphalerite was identified in the Baia Sprie ore deposit associated with minerals formed in the final epithermal phase. It was deposited on idiomorphic crystals of stibnite, which it corrodes. Its structure and an alternate banding, exhibited on the nano-/microscale, were identified by optical microscopy, SEM (scanning electron microscopy), and BSE (backscattered electron microscopy) imaging. These structures are typical for colloform sphalerite and suggest a genesis due to episodic precipitation. The spherical nano/micro-particles (nodules) are characteristic of the colloform sphalerite from Baia Sprie. Raman analysis indicates the presence of a colloform sphalerite with low iron content. The typical diffraction lines for sphalerite were identified in X-ray diffraction: 3.118 Å (111), 1.907 Å (220), 1.627 Å (311). Microprobe analysis certifies the presence of sphalerite with the stoichiometric formula close to ZnS. Iron content is low (0%–0.0613%), but Sb (0.7726%–2.6813%), Pb (0.56%–1.1718%), Bi (0%–0.1227%) are also present. The negative correlation between Zn and Sb suggests the simultaneous deposition from the same epithermal fluids. Valentinite and colloform sphalerite were formed at low temperatures (100–150 °C) at the end of the epithermal process.

Highlights

  • Valentinite and colloform sphalerite are very rare minerals in epithermal deposits

  • We examine the occurrence of valentinite and colloform epithermal ore deposits from the Baia Mare area, Eastern Carpathians

  • We identified valentinite in samples from Baia Sprie and Dealul Crucii

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Summary

Introduction

Valentinite and colloform sphalerite are very rare minerals in epithermal deposits. Valentinite has been discovered in the Dealul Crucii (Crucii Hill) and Baia Sprie ore deposits and colloformMinerals 2020, 10, 121; doi:10.3390/min10020121 www.mdpi.com/journal/minerals Minerals of 1922 of has been discovered in the Dealul Crucii (Crucii Hill) and Baia Sprie ore deposits and colloform sphalerite sphalerite in in Baia Baia SprieSprie ore ore deposits, deposits, respectively respectively (Figure (Figure 1) 1) [1].[1]. Valentinite and colloform sphalerite are very rare minerals in epithermal deposits. Valentinite has been discovered in the Dealul Crucii (Crucii Hill) and Baia Sprie ore deposits and colloform. Minerals 2020, 10, 121; doi:10.3390/min10020121 www.mdpi.com/journal/minerals Minerals of 19. 22 of has been discovered in the Dealul Crucii (Crucii Hill) and Baia Sprie ore deposits and colloform sphalerite sphalerite in in Baia Baia Sprie. Deposits, respectively respectively (Figure (Figure 1) 1) [1]. Hydrothermal ore ore deposits deposits from from Baia Baia. Mare mining district are internationally recognized for the minerals that were first described

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