Valentinite and Colloform Sphalerite in Epithermal Deposits from Baia Mare Area, Eastern Carpathians

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.

Sphalerite Composition in Low- and Intermediate-Sulfidation Epithermal Ore Bodies from the Roșia Montană Au-Ag Ore Deposit, Apuseni Mountains, Romania

“…The clear separation of the Mn-rich and the Fe-rich compositional trends with a gap of the values distribution between the maximum and minimum ranges confirms the partitioning between Fe and Mn in sphalerite as stated by [50]. The new data for the Ros , ia Montană ore deposit and the published EPMA data on sphalerite from the LS, IS, and HS ore deposits in the Apuseni Mountains (Table S1supplementary material) [6,35,46,47] and the Baia Mare district (Table S2-supplementary material) [46,[48][49][50][51][52][53][67][68][69][70] suggest the existence of two major trends of the Fe-Mn ratio (Figure 7), (i.e., 9i) the Mn-rich trend and (ii) the Fe-rich trend.…”

“…The analyzed sphalerite from Ros , ia Montană was Mn-bearing (Mn > 1 wt%) and showed a constant low Cd content (0.13-0.16 wt% in Ag-free sphalerite) and Mn values approximately one order of magnitude greater than the Fe values (Table 2 and Figure 7). supplementary material) [6,35,46,47] and the Baia Mare district (Table S2supplementary material) [46,[48][49][50][51][52][53][67][68][69][70] suggest the existence of two major trends of the Fe-Mn ratio (Figure 7), (i.e., 9i) the Mn-rich trend and (ii) the Fe-rich trend. The Fe content was usually <1 wt% in the Mn-rich trend, and the Mn content was <0.75 wt% in the Fe-rich trend (Figure 7).…”

Phonon Spectroscopy in Antimony and Tellurium Oxides

“…The modes below 400 cm −1 , that is, group † modes, are controlled by the unit cell and crystal space group of the structure, and modes above 400 cm −1 are Sb−O chain stretching modes from the SbO 3 units. 18,83 The uncertainty associated with each peak is 3 cm −1 . note that, strictly speaking, INS data obtained on the VISION spectrometer do not capture the correct DPS, in particular at low energies, because of the limiting sampling in Q-space.…”

“… a The modes below 400 cm –1 , that is, group † modes, are controlled by the unit cell and crystal space group of the structure, and modes above 400 cm –1 are Sb–O chain stretching modes from the SbO 3 units. , The uncertainty associated with each peak is 3 cm –1 . …”