Periodico di Mineralogia

Petrography and mineralogical study of gold mineralization in the Tasiast Archean deposits (Mauritania)

Masbaha Zeine — 2025-01-15

This study aims to determine the mineral phases containing gold mineralization and other mineral indicators in two prominent deposits (West Branch and Piment) in Tasiast. This latter area is one of the major areas of the Reguibat Shield and is primarily composed of Mesoarchean rocks from the Aoueouat greenstone belt. In addition, the West Branch is hosted in meta-igneous rocks, whereas Piment is situated within meta- sedimentary rocks. The results of 55 samples collected from the cores of two boreholes show that the crossed series is composed by rocks of the types felsite (FVC), greywacke (SGW), siltstone (SVC), micaschist (MCS) and banded iron formation (BIF). Petrographic observations via polished and thin sections, scanning electron microscopy (SEM) and cathodoluminescence (CL) confirmed by mineralogical results were performed by means X-ray diffraction (XRD), revealed that the genesis of gold deposits in both boreholes was linked mainly to hydrothermal activity.

The minerals associated with the hydrothermal deposits are biotite, muscovite, fuchsite, zoisite, staurolite, chlorite, cummingtonite, tourmaline, hornblende and garnet. They are present in variable proportions in the crossed rocks, which suffered a high degree of metamorphism. On the other hand, the genesis of gold is mostly linked to hydrothermal activity. In fact, this mineral is associated mainly with sulfides such as pyrrhotite and occasionally appears as inclusions inside pyrite and arsenopyrite. Therefore, the hydrothermal system that generated the gold mineralization was likely active under brittle and ductile deformation conditions after mild metamorphism.

Raman spectral features of a natural chromitite from NW Türkiye: Characterization of magnesiochromite spectra and implications

Mehmet Akbulut — 2025-03-26

In this work, a first detailed Raman spectroscopic measurement study of natural magnesiochromites from a multi-textural ophiolitic chromitite sample from Harmancık district in north-western Türkiye has been presented to characterize the Raman spectral features of Turkish high-Cr ophiolitic chromitites. The magnesiochromites in the multi-textural chromitite sample has an almost uniform composition, with Cr2O3, Al2O3, and TiO2 contents being 62.02 wt%, 9.18 wt%, and 0.14 wt% in average, respectively. Cr#s are 0.82 and Mg#s are 0.65 in average, in the ranges that of typical ophiolitic chromitites of boninitic to arc-related affinity. Despite this uniform composition, three distinctive Raman spectra morphologies (Types I, II and III) are determined. Of these, the Type I spectra is by far the dominant. Three common main band clusters are defined (BG- 1, BG-II and BG-III) for all of the morphological types. The BG-I (~385-605 cm-1) and BG-II (~649-739 cm-1) are the main clusters that incorporate the high intensity and descriptive peaks and shoulders. The BG-III includes the very low intensity broad bands around 1122 to 1763 cm-1, considered as overtones of the BG-I, and BG-II. Four of the several bands in the BG-I and BG-II has been assigned to the A1g (~690 cm-1), F2g(3) (~605 cm-1), F2g(2) (~555 cm-1), and Eg (~470 cm-1) modes of spinel. Of the several un-assigned bands, the ~730 cm-1 band has been interpreted to be related with the high-Cr nature of the studied sample. The variance in this band’s intensity has been interpreted to be related with concomitant or post-crystallization textural arrangement and the plastic mantle deformation. This result emphasize the viability of a preliminary approach on orientation of the magnesiochromites in the ophiolitic chromitites via Raman spectroscopy, if the composition variable can be constrained.

WinCrtclas, a Windows program for cerite-supergroup minerals✝

Fuat Yavuz — 2025-03-28

A Microsoft® Visual Basic software, WinCrtclas, has been developed to calculate the chemical formulas of cerite-supergroup minerals (CSM) based on data obtained from wet-chemical and electron-microprobe analyses. WinCrtclas currently evaluates 17 valid mineral species using the Commission on New Minerals, Nomenclature and Classification (CNMMC) of the International Mineralogical Association (IMA) nomenclature scheme in the general formula A9XM[T7O24Ø4]Z3. The program recalculates the compositional formulas of CSM based on 28 oxygen atoms with the T-site total of 7.00 normalization option. Mineral formulas of the CSM are calculated considering the valency-imposed double site occupancy and the site total charge approach, allowing a double suffix to state the essential A constituents in the general formula. WinCrtclas operates in four stages: (1) it estimates cation and anion contents provided by input chemical data; (2) it determines the dominant cation and anion at the A, X, M, T and Z sites; (3) it assigns the CSM based on the dominant cations and anions at these sites; and (4) it classifies the species into an appropriate groups. WinCrtclas allows users to: (1) enter up to 41 input variables for mineral-chemical analyses; (2) type and load multiple CSM compositions in the data entry section; (3) edit and load the Microsoft® Excel files used in calculating, classifying, and naming the CSM, and (4) store all the calculated parameters in the output of a Microsoft® Excel file for further data evaluations.