Nd-Sr Isotopic Study of Magmatic Rocks and 40Ar/39Ar Dating of the Mafic Dike of the Proterozoic Ulan-Sar’dag Ophiolite Mélange (Southern Siberia, East Sayan, Middle Belt, Russia)

We report the first radiogenic Nd-Sr isotope data in the magmatic rocks island-arc ophiolite assemblage from the middle branch of the East Sayan ophiolite complexes to better constrain geodynamic processes in this segment of the CAOB in southern central Siberia. The magmatic rocks belong to the following geochemical types: (1) Ensimatic island-arc boninites; (2) island-arc assemblage; (3) enriched basalts of mid-ocean ridges; and (4) oceanic island-like basalts. The boninites have a positive value εNd (T), which is generated from a depleted mantle source (N-MORB). The island-arc assemblage has negative or slightly positive εNd (T) and was formed from an enriched mantle source due to the subduction of terrigenous rocks. The source of the terrigenous material was most likely the rocks of the Archean TTG (Trondhjemite Tonalite Granodiorite) complex of the Gargan block. Isotopic ratios for E-MOR and OIB-like basalts are characterized by positive or slightly negative values of εNd (T). The mafic dike, which crosscut ophiolite rocks, corresponds to OIB-like basalts. The values of εNd (T), measured 87Sr/86Sr and I (Sr), in the mafic dike correspond to the EM I mantle source. The E-MOR and OIB-like basalts appear to be formed in late-stage asthenospheric mantle melting via the decompression melting processes. The obtained isotope geochemical data for the E-MOR and OIB-like basalts probably indicate the mixing of island-arc melts with asthenospheric melts. We undertook 40Ar/39Ar dating of the mafic dike, which crosscut the ophiolite unit. The mafic dike has a whole-rock 40Ar/39Ar weighted mean plateau age of 799 ± 11 Ma. The dating constrains the minimum age of the ophiolite and island-arc magmatism in the region.

Mineralogy, Fluid Inclusions, and Isotopic Study of the Kargah Cu-Pb Polymetallic Vein-Type Deposit, Kohistan Island Arc, Northern Pakistan: Implication for Ore Genesis

The Kargah Cu-Pb polymetallic deposit is a newly discovered ore deposit from the Gilgit-Baltistan region, located in the Kohistan Island Arc, northern Pakistan. However, this area is poorly researched on the ore genesis, and its origin and the evolution of its magmatic-hydrothermal system remain unclear. Three stages of mineralization were identified, including quartz-pyrite, quartz-sulfide, and carbonate representing early, middle, and late stages, respectively. The major ore minerals are pyrite, chalcopyrite, galena, and zincian tetrahedrite with minor native silver, and native gold mainly distributed in pyrite. Here, we present a systematic study on ore geology, hydrothermal alterations, trace element composition of pyrite, fluid inclusions, and isotopes (S and Pb) characteristics to gain insights into the nature of the ore-forming fluids, types of unknown deposits, and hydrothermal fluid evolution. The high Co/Ni ratio (1.3–16.4) and Co content (average 1201 ppm), the low Mo/Ni ratio (0.43–0.94) and Mo contents (average 108 ppm) of both Py-I and Py-II suggest a mafic source for the mineralization. The Au-Ni plots, Co-As-Ni correlation, and the δ34S values range from −2.8 to 6.4‰ (average of 3.4‰) indicating the affiliation of the mineralization with a mantle-derived magmatic-hydrothermal provenance. The Pb isotope data showing the narrow variations in 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb values suggest a single lead source from crustal-derived materials. The microthermometry data suggest that the dominant mechanisms are fluid boiling and mixing for mineral precipitation at temperatures ranging between 155 and 555 °C, and represent an intrusion-related magmatic-hydrothermal environment for the Kargah Cu-Pb polymetallic deposit.

An Isotopic Study of Bio-accessible Lead in Wheat, Miswak Toothbrush and Miswak Fruit Using the Continuous On-line Leaching Method with Inductively Coupled Plasma Mass Spectrometry

In this study, sources of Pb are investigated using the 206Pb/207Pb isotopic ratio measured by inductively coupled plasma quadrupole mass spectrometry in the bio-accessible fractions from wheat, Miswak toothbrush (also used as chewing stick) and Miswak fruit. These samples were obtained for the in vitro batch and on-line leaching methods that mimic the human gastrointestinal tract by sequentially using artificial saliva, gastric juice and intestinal fluid for extraction. The two methods provided similar results according to a Student’s t-test at the 95% confidence level. Significant (p < 0.05) differences in 206Pb/207Pb were noted at the 95% confidence level in different artificial body fluids. Except for unpolluted Miswak toothbrush and Miswak fruit, which only contained geogenic Pb, the samples contained a mixture of geogenic and anthropogenic Pb, with bio-accessible Pb in saliva being mainly from a geogenic source, whereas bio-accessible Pb in the stomach and intestinal fluids was mainly from anthropogenic sources. Despite the fact that leaded petrol was phased out in Saudi Arabia in 2001, a Miswak toothbrush collected on the side of a busy road after exposure for only a few days and Safeer wheat were still being contaminated with Pb and had an isotopic composition matching that of Pb added to petrol. The 208Pb/206Pb isotopic ratio for gastric bio-accessible Pb also matched that reported in tetraethyllead. The 206Pb/207Pb isotopic ratios of intestinal bio-accessible Pb from Qassim wheat and Safeer wheat point to coal combustion as the source. Overall, these results highlight the need for continued Pb monitoring and the value of examining bio-accessible fractions periodically to identify Pb sources.

Stable Isotopes Anomalies of Storm Event in April 2019 in Southwestern Iran: A Method to Characterize the Origin of the Atmospheric Masses

To determine the source of April 2019 storm event in south-western Iran, stable isotopic technique (2H and 18O) of precipitation were used. The unique event, with a mean of 230 mm/year, i.e. 46% of the annual rainfall over four days, caused large dams on Dez and Karkheh rivers to overflow and a great deal of casualties and financial losses. To determine the characteristics of stable isotopes 2H and 18O of this event, 43 samples of rain water were collected in the area about 41,000 (Km)2 in south-western Iran with altitudes between zero to 2814 m (m.a.s.l). The local meteoric water line (LMWL) was prepared during the storm event and compared with the global, Mediterranean and other parts of Iran as well as neighbouring countries. According to the LMWL equation (δ2H = 6.5996 δ 18O + 7.561) and d-excess (with average 7.85 ‰), the source of precipitation was the integration of the meteoric masses of Mediterranean and Red Sea. There was a low correlation between the altitude increase and the 18O decrease (0.13 per 100 meters), which is a characteristic of this storm event. This isotopic study has proven the impact of Sudanese mass on the occurrence of storm event in south-western Iran for the first time isotopically.