Elitsa Stefanova

The Djurkovo and Govedarnika deposits represent hydrothermal Pb-Zn systems spatially associated with the Eocene–Oligocene tectono-magmatic evolution of the Rhodope Metamorphic Complex. This study presents new mineralogical and geochemical data for galena, sphalerite, pyrite, and chalcopyrite obtained by electron probe microanalysis (EPMA) and LA-ICP-MS in order to evaluate the compositional variations of sulphides among the vein and metasomatic mineralization types and between the two deposits. The analysed sulphides exhibit distinct compositional signatures reflecting the different mineralization stages and hydrothermal environments. Sphalerite from the Govedarnika metasomatic ores is enriched in Mn (up to 5200 ppm), Fe (up to 5.13 wt.%) and Co due to interaction with Mn-rich skarn assemblages, whereas Djurkovo sphalerite shows elevated Cd (up to 3000 ppm), In and Hg concentrations. Trace-element systematics indicate coupled Fe-Mn incorporation, competitive Cd-Fe substitution and local re-equilibration processes associated with “chalcopyrite disease” textures. Late pyrite from the quartz-carbonate stage is enriched in As (up to 3.87 wt.%), Au (up to 78 ppm), Ag, Se, Sb and Tl, with positive Au-As and Au-Ag correlations suggesting invisible gold and possible submicroscopic precious-metal inclusions. The obtained data demonstrate prolonged hydrothermal evolution and highlight the potential role of the studied sulphides as concentrators of economically important elements.

Apatite is a widespread accessory mineral, which can provide information on the geochemical characteristics of magma and the conditions of hydrothermal alteration of the rocks in magmatic–hydrothermal deposits. This study aims to understand the relationships between the geochemical and textural features of apatites from diorite porphyries that have undergone different degrees of hydrothermal alteration in the Sharlo Dere area, Chelopech epithermal Cu-Au deposit, Bulgaria. The apatites were characterized by laser ablation–inductively coupled plasma mass spectrometry, scanning electron microscopy with energy-dispersive X-ray spectroscopy, electron probe microanalysis with wave-dispersive spectroscopy, optical cathodoluminescence and multi-element mapping. Magmatic apatites from “hematitic”, propylitic and propylitic-sericitic zones of alteration are distinguished by euhedral crystals with oscillatory zoning and brown luminescence in CL images. In quartz-sericitic alteration zones, apatite has a yellow CL response. Hydrothermally altered apatites in the diorite porphyries overprinted by advanced argillic alteration have corroded, irregular forms and pink-green luminescence. Apatite crystals of magmatic origin reveal high contents of chlorine, strontium, light rare earth elements (LREE), negative Eu anomalies and high La_N/Sm_N and Ce_N/Yb_N ratios. Hydrothermally altered or hydrothermal apatites are distinguished by their higher contents of Na₂O, F, SO₃, Y and middle rare earth elements (MREEs) and their low La_N/Sm_N and Ce_N/Yb_N ratios. The intensity of hydrothermal alteration affects the luminescence and major and trace element contents, including the rare earth element patterns in the apatites, implying apatite can be used as a geochemical indicator to study magmatic–hydrothermal ore deposits.

Deep-sea Fe-Mn polymetallic nodules formed nowadays at the deep-sea ocean floor were evaluated as promising critical raw materials (CRMs). Here, we report results of polymetallic nodules from the H22_NE block of the Interoceanmetal (IOM) exploration area in the eastern part of the Clarion–Clipperton Zone (CCZ), NE Pacific Ocean. The polymetallic nodules were studied with X-ray Diffraction, Raman spectroscopy, SEM-EDS, and LA-ICP-MS (bulk nodules and in situ nodule layers). Additionally, we combine geochemical data of polymetallic nodules with the previously reported data of pore waters and sediments from six stations. Our study aims to define the mineral composition and determine the content of CRMs in the polymetallic nodules and to assess the main factors controlling metal deposition and nodule enrichment in some CRMs. Mn content and the Mn/Fe ratio of the nodules classify them mostly as mixed hydrogenetic–diagenetic type. They are also enriched in Ni, Cu, Co, Zn, Mo, W, Li, Tl, and REE. The in situ REE patterns exhibit MREE and HREE enrichment and a variable Ce anomaly that argues for a changing oxic/suboxic environment and periodically changing of diagenetic and hydrogenetic nodule growth. The results of the joint study of the bottom sediments, pore waters, and polymetallic nodules show a complexity of processes that influence the formation of these deposits. The changing oxic and anoxic conditions are well documented in the chemistry of the nodule layers. Probably the most important controlling factors are sedimentation rate, bioturbation, adsorption, desorption, and oxidation. In addition, growth rates, water depth variations, electro-chemical speciation, phosphatization, and the structures of the Fe-Mn adsorbents are also considered. The polymetallic nodule deposits in the IOM contract area are estimated for future mining for Ni, Cu, Co, and Mn resources. They, however, contain additional metals of economic importance, such as REE and other trace elements (referred to as CRMs) that are potential by-products for metal mining. They can significantly increase the economic importance of exploited polymetallic nodules.

White mica (sericite) is one of the most common minerals in the hydrothermal alteration types at the Elatsite deposit. Differences in the mineral chemistry of sericite revealed some characteristics of the hydrothermal fluid environment. Lowest values of phengite component are determined in sericite from quartz-sericitic alteration, while higher phengite component with lower values for Na2O are reported in sericite from quartz-adularia-carbonate alterations. This probably reflects lower temperature formation from fluids with relatively high pH (close to the neutral) for sericite from quartz-adularia-carbonate alteration compared to this from quartz-sericitic alteration.

The Elatsite porphyry-copper deposit is one of the largest and well-studied deposits in Bulgaria. The mineralization and hydrothermal alteration are related to Late Cretaceous magmatic activity associated with the Late Alpine evolution of the area. The three of the most common alteration types are K-silicate, K-silicate-sericitic and quartz-sericitic alteration. The three alterations have complicated relationships and in most cases are superimposed on each other, which makes field studies and petrographic observations difficult. The geochemical data for altered rocks can provide useful information and further be used as a geochemical tool for accurate determination of the alteration. One way of representing this geochemical data is by calculating the „Alteration indices“. These indices represent ratios of the major elements oxides and here we present data for three Alteration indices (AI 1, AI 2 and CCPI). Our results suggest that the increase of the AI 1 and the decrease of the AI 2 and CCPI for the K-silicate, K-silicate-sericitic and quartz-sericitic alterations compared to the unaltered rocks are related to the gain of K2O and MgO and the loss of CaO and Na2O during the alteration process. The graphical construction of juxtaposition of two Alteration indices provides a useful tool for accurate distinction of the three most common alteration types of the Elatsite PCD.

Mineralogical and geochemical LA-ICP-MS trace element study was conducted on sulphides from the Djurkovo Pb-Zn deposit, Central Rhodopes. The studied ore mineralization consists mainly of sphalerite, galena, pyrite, and chalcopyrite precipitated in three mineral parageneses, part of the main polymetallic and quartz-carbonate stages as it is indicated by the textural relationships. The first paragenesis is developed as massive metasomatic replacement occurring in the marble horizons and consisting of sphalerite, galena, and chalcopyrite. The second para­genesis represents later veins composed mainly of quartz, pyrite, galena, and sphalerite crosscutting the metasomatic bodies. The third paragenesis represents late thin carbonate veins with translucent greenish sphalerite (cleiophane) and pyrite/marcasite aggregations, parts of the quartz-carbonate stage. The trace element signatures of the studied sphalerites indicate incorporation of Fe, Cd, Mn, Cu, Co, In, and Hg. Important elements in pyrites are Co, As, Pb, Mn, and Se. Chalcopyrite is the main carrier of Ag among the studied sulphides. The latest pyrite/marcasite aggregations show significant incorporations of As, Sb, and Tl.

Assarel porphyry copper deposit is located in the Panagyurishte ore district, Central Srednogorie, which is a part of the Late Cretaceous Apuseni–Banat–Timok–Srednogorie magmatic and metallogenic belt. This study reports a new data on the epithermal high-sulfidation ore mineralization described previously as “specific” and “rare”. The ore mineralization is associated with advanced argillic alteration and is represented by enargite, colusite, sulvanite, bornite. They occur as thin veinlets brecciating or crosscutting earlier small disseminated euhedral/subhedral to anhedral pyrite in quartz or subhedral/anhedral pyrite nest-like aggregates with zunyite, gypsum, rutile. Bornite is replaced by chalcocite and covellite, and enargite by covellite. Enargite contains Sn, Sb, Te, while colusite occurs as two distinct chemical varieties: 1) Sn-rich and Mo-bearing, with lower As content, and 2) Sn-poor, Ge-bearing, As-rich. Both varieties have 0.1–0.2 wt% Sb. Bornite and chalcocite contain small amounts of Se. Pyrite spatially associated with this mineralization is enriched in Cu, Co, and Ni, with Co/Ni and Co/As ≥ 2.

The Djurkovo base-metal vein deposit in Laki ore field, is hosted by a heterogeneous gneiss/amphibolite/marble rock sequence of the high-grade metamorphic complex of the Central Rhodopes. Mineralogical and geochemical investigation was conducted on slightly deformed, and hydrothermally altered thin pegmatite dykes intruded in the marbles. The pegmatite bodies consist mostly of K-feldspar, albite and quartz, with minor garnet present. Clear textural zonation within the bodies is absent except for the preferential crystallization of garnet in the innermost parts. The main pegmatite accessories include ishikawaite, zircon, apatite, monazite-(Ce), allanite-(Ce), and titanite. The post-magmatic hydrothermal overprint on the pegmatites resulted in the formation of the assemblage including epidote, sericite, chlorite, carbonate, quartz, hematite, and leucoxene. The accessory oxide, silicate, and phosphate minerals bearing rare earth elements (REE), actinides (ACT), Nb, Ta, and Ti have undergone partial replacement by secondary mineral phases (thortveitite, fergusonite, fersmite, uraninite, thorianite, REE-epidote, xenotime) observed as irregular grains or veinlets along fractures and dissolved zones, either inside or near the primary minerals.