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Papers by Strashimir Strashimirov

Research paper thumbnail of Mineral composition of the Late Cretaceous Breznik-Bardoto Au epithermal ore occurence (preliminary data), Western Srednogorie Belt, Bulgaria

Research paper thumbnail of An Ultrasonic Probe for the Extraction of Microscopic Quantities of Minerals for X-ray Work

Mineralogical Magazine, 1996

The instrumentation and procedure is described for the extraction of very small and pure samples ... more The instrumentation and procedure is described for the extraction of very small and pure samples from polished mounts and thin sections of minerals, for X-ray analysis and other micro-analytical techniques. It uses a stand-mounted, tunable ultrasonic probe (400 W/15–50 kHz) inclined at 45°C to a microscope stage. The tip of the probe, usually a steel needle, is located on the desired mineral and an appropriate ultrasonic frequency is selected. Very fine powders are produced from grains as small as 0.01–0.005 mm. A distinct advantage of this technique is that, as different minerals powder at different rates and different frequencies, it is possible to separate a single mineral from an intergrowth of two or more minerals.

Research paper thumbnail of Porphyry Systems of the Panagyurishte Ore Region

Research paper thumbnail of MAIN FEATURES IN GEOLOGY AND METALLOGENY OF THE PANAGYURISHTE ORE REGION

The Panagyurishte ore district is located in the Central Sredna Gora and partly in the Stara Plan... more The Panagyurishte ore district is located in the Central Sredna Gora and partly in the Stara Planina mountains. It is an element of the Upper Cretaceous Apyseni-Banat-Timok-Srednogorie Magmatic and Metallogenic Belt. Forming of this ore region is determined by the development of intensive Upper Cretaceous volcanic and magmatic activity. Magmatic rocks belong to two petrochemical series: calc-alkaline and subalkaline ones. Magma generation took place in enriched upper mantle with variegating participation of crustal component. It is established following well expressed volcano-intrusive complexes: Elatsite-Chelopech, Krassen-Petelovo, Vrankamik, Assarel-Medet, Svoboda-Ovchihulm, Elshitsa and Pesovetz. Magmatic activity is realised during Conniasian-Santonnian and the distinct migration from north to south is established. Ore fields include Elatsite-Chelopech, Krassen-Petelovo, Assarel-Medet, Radka and Elshitsa. Metallogenic specialisation of the region is determined by numerous Cu, Cu-Mo and Cu-Au porphyry deposits associating with high to intermediate sulphidation epi-to mesothermal massive sulphgide Cu-Au, Cu-Pyr-Au and Cu-Pyr deposits. Intermediate to low sulphidation Cu, Pb-Zn-(+ Au), Cu-Pb-Zn--(+ Au), Au и Ba deposits related to brittle faulting are developed in the marginal parts of the ore fields. Mn ore occurrences type "silicified umbra" are found in volcano-sediment rocks in the region.

Research paper thumbnail of Geology and Metallogeny of the Srednogorie Zone and Panagyurishte Ore Region

Research paper thumbnail of U–Pb dating, Hf-isotope characteristics and trace-REE-patterns of zircons from Medet porphyry copper deposit, Bulgaria: implications for timing, duration and sources of ore-bearing magmatism

Mineralogy and Petrology, 2009

Precise U-Pb geochronology, Hf isotope compositions and trace element distributions in zircons ar... more Precise U-Pb geochronology, Hf isotope compositions and trace element distributions in zircons are combined in the present study to define the timing and sources of the magmatism forming the Medet porphyry copper deposit, Bulgaria. ID-TIMS U-Pb-zircon dating demonstrates that ore-bearing magmatism extended for less than 1.12 Ma. As inferred from the field relationships, it started with the intrusion of a quartz-monzodiorite at 90.59± 0.29 Ma followed by granodiorite porphyries at 90.47±0.30 and 90.27±0.60 Ma and by crosscutting aplite dykes at 90.12±0.36 Ma. These units were overprinted by potassic alteration and host economic copper-(Mo-Au) mineralization. The main magmatic-hydrothermal activity ceased after that, and a later quartz-granodiorite porphyry dyke, dated at 89.26±0.32 Ma, only contains an uneconomic quartz-pyrite mineralization. Assimilation of Lower Paleozoic rocks with a mantle to mantle-crust signature is characteristic of the fertile magma in the Medet deposit, as defined by positive ɛ-Hf values of the inherited zircons. The positive Ce-anomalies and the higher Eu/Eu* ratios of the zircons in the mineralized Cretaceous rocks of Medet deposit argue for crystallization from a generally more oxidized magma compared to the later quartz-granodiorite porphyry dyke. A change in paleostress conditions occurred during the intrusion of the Medet pluton and its dykes. The initial stage reveals E-W extension associated with N-S compression, whereas the younger granodiorite dyke was emplaced during subsequent N-S extension. The large-scale switch of the extensional stress regime during the mineralization was favourable for ore deposition by channelling the fluids and increasing the effective permeability.

Research paper thumbnail of Porphyry-copper mineralisation in the central Srednogorie zone, Bulgaria

Mineralium Deposita, 2002

The porphyry-copper systems in the central part of the Srednogorie zone (Bulgaria) are represente... more The porphyry-copper systems in the central part of the Srednogorie zone (Bulgaria) are represented by three major deposits (Elatsite, Medet and Assarel) and several smaller deposits and occurrences, all of them within the Panagyurishte ore district. The hydrothermal systems are related to Late Cretaceous calc-alkaline igneous complexes. Ore mineralisation is developed predominantly in the apical parts of subvolcanic and intrusive bodies as well as within the volcanic and basement metamorphic rocks. Several of the porphyry systems are spatially associated with shallow-level intermediate and high-sulphidation volcanic-hosted epithermal deposits of economic importance, such as the major gold-copper mine at Chelopech located 10 km from the Elatsite porphyry-copper deposit. Mineralisation processes in the porphyry deposits start with intensive hydrothermal alteration of the wall rocks. K-silicate alteration is characteristic for pre-ore hydrothermal activity in all of them, and it is located mostly in their central parts. Propylitic alteration is prominent in the Medet and Assarel deposits. The Assarel deposit is located in the central part of a palaeovolcanic structure and shows a large spectrum of pre-ore alterations, including propylitic, sericitic, and advanced argillic assemblages. The initial stages of the hydrothermal systems are characterised by high temperatures (>550-500°C) and highly saline (50-20 wt% NaCl equiv.) and vapour-rich fluids of likely magmatic origin. The composition of the fluids gradually changes from H 2 O-NaCl±FeCl 2 to H 2 O-NaCl-KCl and H 2 O-NaCldominated as the fluids cool, react with wall rocks, and may become diluted with meteoric water. Fe-Ti-oxide mineral associations were formed early in all deposits, later followed, in the Elatsite deposit, by an assemblage of bornite, chalcopyrite, platinum group element (PGE) phases, Co-Ni thiospinels, Ag-and Bi-tellurides, and selenides. The main ore stage in all deposits is dominated by chalcopyrite ± pyrite, associated with propylitic alteration at Medet, K-silcate-sericite alteration at Elatsite, and chlorite-sericite alteration at Assarel. Specific geochemical features of the ore systems are marked by precipitation of numerous fine-grained mineral inclusions in chalcopyrite and pyrite (palladoarsenide, Pd-rammelsbergite, Cu-Ni sulpharsenides in Elatsite; Co-and Ni-pyrite, carrolite, vaesite, sulvanite and colusite in Medet; enargite, As-sulvanite, colusite, goldfieldite, wittichenite, calaverite and aikinite in Assarel). Native gold and electrum are observed as small grains, except in Elatsite where larger aggregates up to several millimetres are found. Molybdenite is present as small flakes within chalcopyrite, or forms felted aggregates within thin quartz veinlets in the Elatsite and Medet deposits, and very rarely at Assarel. Thin veinlets of quartz-galena-sphalerite are found at the upper parts of the deposits. Supergene alteration of the primary sulphide minerals is developed in the Assarel deposit where a thick blanket of secondary copper mineralisation (chalcocite, covellite) has formed. In the other two deposits, secondary mineral associations (Cu and Fe oxides and hydroxides) are limited to near the surface. Differences in the deposits studied suggest that Elatsite and Medet are formed probably at deeper levels of the porphyry systems, whereas Assarel is developed at rather shallower and lower-temperature conditions typical of the apical part of a subvolcanic body intruding its volcanic superstructure.

Research paper thumbnail of Geochemical and Sr-Nd isotope constraints on the Late Cretaceous magmatism in the area of the Zidarovo ore field

The Zidarovo ore field is situated 15-20 km south from the town of Bourgas. The region consists o... more The Zidarovo ore field is situated 15-20 km south from the town of Bourgas. The region consists of Senonian volcanic, intrusive and sedimentary rocks. The syn-/postmagmatic hydrothermal activity was responsible for the formation of polymetallic and gold-polymetallic ore veins in the volcanic rocks. The ore mineralisation is developed in two sectors -Kanarata in the central part (close to the Zidarovo intrusive) and Yurta in the NNW part of the ore field. The composition of the volcanic rocks of the Zidarovo ore field varies from basaltic to trachy-andesitic. The sub-volcanic dyke complex has basaltic and trachy-basaltic composition, and the intrusive rocks are gabbroic to monzo-dioritic. The rock varieties belong to the high-K calc-alkaline magmatic series. Indicative bivariate diagrams as Nb vs. Y, Rb vs. (Y+Nb), Rb vs. (Yb+Ta) and Zr/Al2O3 vs. TiO2/Al2O3 define volcanic-arc tectonic environment of their formation. MORB normalized trace elements patterns of the magmatic rocks (enrichment of large ion lithophile elements and low values for high field strength elements, the strong negative Ta and Nb anomaly and the chondrite-normalized REE distribution of the basaltic rocks indicate subduction related magma affinity. Nd and Sr whole rock isotope data are in agreement with this conclusion revealing mantle-crustal signatures with ε-Nd (80 Ma) values generally between +2.1 and +3.0 and initial strontium ratios in the narrow range 0.704-0.705. Compared with the data for the Central Srednogorie the magmatic rocks from the Zidarovo ore field are less crustal contaminated. The same trend is observed comparing intrusive and volcanic varieties -the volcanic rocks reveal more primitive isotope composition, which is explained by the faster cooling of the volcanites, probably prior to contamination with crustal materials in middle/upper crustal chambers. ; rouskov@mgu.bg, 2 Институт по изотопна геохимия и минерални ресурси, ETH, CH-8092 Цюрих; quadt@erdw.ethz.ch 3 Централна лаборатория по минералогия и кристалография "Акад. Иван Костов", БАН, София1113; peytcheva@erdw.ethz РЕЗЮМЕ. Зидаровското рудно поле е разположено на около 15-20 км. южно от гр. Бургас. Районът е изграден предимно от сенонски вулканогенни, интрузивни и седиментни скали. Резултат от постмагматични хидротермални процеси са жилите с полиметални и злато-полиметални руди във вулканските скали. Рудната минерализация е развита в два участъка -Канарата в централната част (в близост до Зидаровския интрузив) и Юрта в северсеверозаданата част на руднотото поле. Съставът на вулканските скали в Зидаровското рудно поле варира от базалти до трахиандезити. Субвулканският дайков комплекс има базалтов и трахибазалтов, a интрузивните скали -габров до монцо-диоритов състав. Скалите принадлежат основно към високо калиевата калциево-алкална магматична серия. Индикативни диаграми като Nb vs. Y, Rb vs. (Y+Nb), Rb vs. (Yb+Ta) и Zr/Al2O3 vs. TiO2/Al2O3 определят островно-дъгова обстановка на формиране. MORB нормализираните разпределения на редките елементи в скалите (обогатяване на LILE и ниски стойности за HFSE), добре изразената негативна Ta и Nb аномалия и хондрит-нормализираните разпределения РЗЕ (обогатяване на LREE) определят субдукционна обстановка на формиране. Nd и Sr изотопни данни подкрепят този извод като показват мантийно-корови характеристики с ε-Nd (80 Ma) стойности основно между +2.1 и +3.0 и начални стронциеви отношения предимно в тесния интервал 0.704-0.705. В сравнение с данните от централното Средногорие магматичните скали от Зидаровското рудно поле са по-малко корово контаминирани. Същият тренд се наблюдава при сравняването на интрузивните и вулкански скали -вулканските скали показват по-примитивни изотопни състави, което се обяснява с по-бързата кристализация на вулканитите, вероятно преди контаминирането им с корови материали в средно/горно корови магмени камери.

Research paper thumbnail of Mineral composition of the Late Cretaceous Breznik-Bardoto Au epithermal ore occurence (preliminary data), Western Srednogorie Belt, Bulgaria

Research paper thumbnail of An Ultrasonic Probe for the Extraction of Microscopic Quantities of Minerals for X-ray Work

Mineralogical Magazine, 1996

The instrumentation and procedure is described for the extraction of very small and pure samples ... more The instrumentation and procedure is described for the extraction of very small and pure samples from polished mounts and thin sections of minerals, for X-ray analysis and other micro-analytical techniques. It uses a stand-mounted, tunable ultrasonic probe (400 W/15–50 kHz) inclined at 45°C to a microscope stage. The tip of the probe, usually a steel needle, is located on the desired mineral and an appropriate ultrasonic frequency is selected. Very fine powders are produced from grains as small as 0.01–0.005 mm. A distinct advantage of this technique is that, as different minerals powder at different rates and different frequencies, it is possible to separate a single mineral from an intergrowth of two or more minerals.

Research paper thumbnail of Porphyry Systems of the Panagyurishte Ore Region

Research paper thumbnail of MAIN FEATURES IN GEOLOGY AND METALLOGENY OF THE PANAGYURISHTE ORE REGION

The Panagyurishte ore district is located in the Central Sredna Gora and partly in the Stara Plan... more The Panagyurishte ore district is located in the Central Sredna Gora and partly in the Stara Planina mountains. It is an element of the Upper Cretaceous Apyseni-Banat-Timok-Srednogorie Magmatic and Metallogenic Belt. Forming of this ore region is determined by the development of intensive Upper Cretaceous volcanic and magmatic activity. Magmatic rocks belong to two petrochemical series: calc-alkaline and subalkaline ones. Magma generation took place in enriched upper mantle with variegating participation of crustal component. It is established following well expressed volcano-intrusive complexes: Elatsite-Chelopech, Krassen-Petelovo, Vrankamik, Assarel-Medet, Svoboda-Ovchihulm, Elshitsa and Pesovetz. Magmatic activity is realised during Conniasian-Santonnian and the distinct migration from north to south is established. Ore fields include Elatsite-Chelopech, Krassen-Petelovo, Assarel-Medet, Radka and Elshitsa. Metallogenic specialisation of the region is determined by numerous Cu, Cu-Mo and Cu-Au porphyry deposits associating with high to intermediate sulphidation epi-to mesothermal massive sulphgide Cu-Au, Cu-Pyr-Au and Cu-Pyr deposits. Intermediate to low sulphidation Cu, Pb-Zn-(+ Au), Cu-Pb-Zn--(+ Au), Au и Ba deposits related to brittle faulting are developed in the marginal parts of the ore fields. Mn ore occurrences type "silicified umbra" are found in volcano-sediment rocks in the region.

Research paper thumbnail of Geology and Metallogeny of the Srednogorie Zone and Panagyurishte Ore Region

Research paper thumbnail of U–Pb dating, Hf-isotope characteristics and trace-REE-patterns of zircons from Medet porphyry copper deposit, Bulgaria: implications for timing, duration and sources of ore-bearing magmatism

Mineralogy and Petrology, 2009

Precise U-Pb geochronology, Hf isotope compositions and trace element distributions in zircons ar... more Precise U-Pb geochronology, Hf isotope compositions and trace element distributions in zircons are combined in the present study to define the timing and sources of the magmatism forming the Medet porphyry copper deposit, Bulgaria. ID-TIMS U-Pb-zircon dating demonstrates that ore-bearing magmatism extended for less than 1.12 Ma. As inferred from the field relationships, it started with the intrusion of a quartz-monzodiorite at 90.59± 0.29 Ma followed by granodiorite porphyries at 90.47±0.30 and 90.27±0.60 Ma and by crosscutting aplite dykes at 90.12±0.36 Ma. These units were overprinted by potassic alteration and host economic copper-(Mo-Au) mineralization. The main magmatic-hydrothermal activity ceased after that, and a later quartz-granodiorite porphyry dyke, dated at 89.26±0.32 Ma, only contains an uneconomic quartz-pyrite mineralization. Assimilation of Lower Paleozoic rocks with a mantle to mantle-crust signature is characteristic of the fertile magma in the Medet deposit, as defined by positive ɛ-Hf values of the inherited zircons. The positive Ce-anomalies and the higher Eu/Eu* ratios of the zircons in the mineralized Cretaceous rocks of Medet deposit argue for crystallization from a generally more oxidized magma compared to the later quartz-granodiorite porphyry dyke. A change in paleostress conditions occurred during the intrusion of the Medet pluton and its dykes. The initial stage reveals E-W extension associated with N-S compression, whereas the younger granodiorite dyke was emplaced during subsequent N-S extension. The large-scale switch of the extensional stress regime during the mineralization was favourable for ore deposition by channelling the fluids and increasing the effective permeability.

Research paper thumbnail of Porphyry-copper mineralisation in the central Srednogorie zone, Bulgaria

Mineralium Deposita, 2002

The porphyry-copper systems in the central part of the Srednogorie zone (Bulgaria) are represente... more The porphyry-copper systems in the central part of the Srednogorie zone (Bulgaria) are represented by three major deposits (Elatsite, Medet and Assarel) and several smaller deposits and occurrences, all of them within the Panagyurishte ore district. The hydrothermal systems are related to Late Cretaceous calc-alkaline igneous complexes. Ore mineralisation is developed predominantly in the apical parts of subvolcanic and intrusive bodies as well as within the volcanic and basement metamorphic rocks. Several of the porphyry systems are spatially associated with shallow-level intermediate and high-sulphidation volcanic-hosted epithermal deposits of economic importance, such as the major gold-copper mine at Chelopech located 10 km from the Elatsite porphyry-copper deposit. Mineralisation processes in the porphyry deposits start with intensive hydrothermal alteration of the wall rocks. K-silicate alteration is characteristic for pre-ore hydrothermal activity in all of them, and it is located mostly in their central parts. Propylitic alteration is prominent in the Medet and Assarel deposits. The Assarel deposit is located in the central part of a palaeovolcanic structure and shows a large spectrum of pre-ore alterations, including propylitic, sericitic, and advanced argillic assemblages. The initial stages of the hydrothermal systems are characterised by high temperatures (>550-500°C) and highly saline (50-20 wt% NaCl equiv.) and vapour-rich fluids of likely magmatic origin. The composition of the fluids gradually changes from H 2 O-NaCl±FeCl 2 to H 2 O-NaCl-KCl and H 2 O-NaCldominated as the fluids cool, react with wall rocks, and may become diluted with meteoric water. Fe-Ti-oxide mineral associations were formed early in all deposits, later followed, in the Elatsite deposit, by an assemblage of bornite, chalcopyrite, platinum group element (PGE) phases, Co-Ni thiospinels, Ag-and Bi-tellurides, and selenides. The main ore stage in all deposits is dominated by chalcopyrite ± pyrite, associated with propylitic alteration at Medet, K-silcate-sericite alteration at Elatsite, and chlorite-sericite alteration at Assarel. Specific geochemical features of the ore systems are marked by precipitation of numerous fine-grained mineral inclusions in chalcopyrite and pyrite (palladoarsenide, Pd-rammelsbergite, Cu-Ni sulpharsenides in Elatsite; Co-and Ni-pyrite, carrolite, vaesite, sulvanite and colusite in Medet; enargite, As-sulvanite, colusite, goldfieldite, wittichenite, calaverite and aikinite in Assarel). Native gold and electrum are observed as small grains, except in Elatsite where larger aggregates up to several millimetres are found. Molybdenite is present as small flakes within chalcopyrite, or forms felted aggregates within thin quartz veinlets in the Elatsite and Medet deposits, and very rarely at Assarel. Thin veinlets of quartz-galena-sphalerite are found at the upper parts of the deposits. Supergene alteration of the primary sulphide minerals is developed in the Assarel deposit where a thick blanket of secondary copper mineralisation (chalcocite, covellite) has formed. In the other two deposits, secondary mineral associations (Cu and Fe oxides and hydroxides) are limited to near the surface. Differences in the deposits studied suggest that Elatsite and Medet are formed probably at deeper levels of the porphyry systems, whereas Assarel is developed at rather shallower and lower-temperature conditions typical of the apical part of a subvolcanic body intruding its volcanic superstructure.

Research paper thumbnail of Geochemical and Sr-Nd isotope constraints on the Late Cretaceous magmatism in the area of the Zidarovo ore field

The Zidarovo ore field is situated 15-20 km south from the town of Bourgas. The region consists o... more The Zidarovo ore field is situated 15-20 km south from the town of Bourgas. The region consists of Senonian volcanic, intrusive and sedimentary rocks. The syn-/postmagmatic hydrothermal activity was responsible for the formation of polymetallic and gold-polymetallic ore veins in the volcanic rocks. The ore mineralisation is developed in two sectors -Kanarata in the central part (close to the Zidarovo intrusive) and Yurta in the NNW part of the ore field. The composition of the volcanic rocks of the Zidarovo ore field varies from basaltic to trachy-andesitic. The sub-volcanic dyke complex has basaltic and trachy-basaltic composition, and the intrusive rocks are gabbroic to monzo-dioritic. The rock varieties belong to the high-K calc-alkaline magmatic series. Indicative bivariate diagrams as Nb vs. Y, Rb vs. (Y+Nb), Rb vs. (Yb+Ta) and Zr/Al2O3 vs. TiO2/Al2O3 define volcanic-arc tectonic environment of their formation. MORB normalized trace elements patterns of the magmatic rocks (enrichment of large ion lithophile elements and low values for high field strength elements, the strong negative Ta and Nb anomaly and the chondrite-normalized REE distribution of the basaltic rocks indicate subduction related magma affinity. Nd and Sr whole rock isotope data are in agreement with this conclusion revealing mantle-crustal signatures with ε-Nd (80 Ma) values generally between +2.1 and +3.0 and initial strontium ratios in the narrow range 0.704-0.705. Compared with the data for the Central Srednogorie the magmatic rocks from the Zidarovo ore field are less crustal contaminated. The same trend is observed comparing intrusive and volcanic varieties -the volcanic rocks reveal more primitive isotope composition, which is explained by the faster cooling of the volcanites, probably prior to contamination with crustal materials in middle/upper crustal chambers. ; rouskov@mgu.bg, 2 Институт по изотопна геохимия и минерални ресурси, ETH, CH-8092 Цюрих; quadt@erdw.ethz.ch 3 Централна лаборатория по минералогия и кристалография "Акад. Иван Костов", БАН, София1113; peytcheva@erdw.ethz РЕЗЮМЕ. Зидаровското рудно поле е разположено на около 15-20 км. южно от гр. Бургас. Районът е изграден предимно от сенонски вулканогенни, интрузивни и седиментни скали. Резултат от постмагматични хидротермални процеси са жилите с полиметални и злато-полиметални руди във вулканските скали. Рудната минерализация е развита в два участъка -Канарата в централната част (в близост до Зидаровския интрузив) и Юрта в северсеверозаданата част на руднотото поле. Съставът на вулканските скали в Зидаровското рудно поле варира от базалти до трахиандезити. Субвулканският дайков комплекс има базалтов и трахибазалтов, a интрузивните скали -габров до монцо-диоритов състав. Скалите принадлежат основно към високо калиевата калциево-алкална магматична серия. Индикативни диаграми като Nb vs. Y, Rb vs. (Y+Nb), Rb vs. (Yb+Ta) и Zr/Al2O3 vs. TiO2/Al2O3 определят островно-дъгова обстановка на формиране. MORB нормализираните разпределения на редките елементи в скалите (обогатяване на LILE и ниски стойности за HFSE), добре изразената негативна Ta и Nb аномалия и хондрит-нормализираните разпределения РЗЕ (обогатяване на LREE) определят субдукционна обстановка на формиране. Nd и Sr изотопни данни подкрепят този извод като показват мантийно-корови характеристики с ε-Nd (80 Ma) стойности основно между +2.1 и +3.0 и начални стронциеви отношения предимно в тесния интервал 0.704-0.705. В сравнение с данните от централното Средногорие магматичните скали от Зидаровското рудно поле са по-малко корово контаминирани. Същият тренд се наблюдава при сравняването на интрузивните и вулкански скали -вулканските скали показват по-примитивни изотопни състави, което се обяснява с по-бързата кристализация на вулканитите, вероятно преди контаминирането им с корови материали в средно/горно корови магмени камери.