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5. Geological and hypogene mineralization characteristics of the hematite‐rich Pelusa IOCG prospect, Antofagasta Region, Northern Chile.

Author

Carvajal, Nicolás, Kojima, Shoji, Vallejo, Alejandro, and Ildefonso, Freddy

Subjects
*ANDESITE, *IGNEOUS rocks, *FLUID inclusions, *MINERALIZATION, *SULFIDE minerals, *VOLCANIC ash, tuff, etc., *PYRITES
Abstract

The Japón, Tailandia and China Sur deposits in the Pelusa mineralized area correspond to a hematite‐dominant IOCG clan within the coastal Cordillera in the Antofagasta Region, Northern Chile, and their mineralization occurs in basaltic to andesitic volcanic rocks of the Jurassic La Negra Formation. In addition to geological and mineralogical descriptions, bulk chemistry of the host rocks, microthermometric and sulfur isotropic analyses were performed to elucidate ore‐forming characteristics of the three orebodies. Chemical data of the host rocks indicate a subalkaline calc‐alkaline affinity with enrichment of the incompatible LILEs, displaying a typical pattern of igneous rocks formed in subduction zones as a general characteristic of the Jurassic‐Lower Cretaceous magmatic arc. Chalcopyrite is the predominant hypogene copper mineral, that variously occurs as veinlets, disseminations and breccia matrix. Fluid inclusions data indicate formation temperatures of the hypogene mineralization ranging mostly from 186 to 377°C, with a high‐salinity range of 30.1 and 45.0 wt% NaCl. The sulfur isotopic ratios (δ34SCDT) of pyrite and chalcopyrite present a narrow range of values from −10.6 to −7.5‰. The negative values in the limited range imply that sulfide minerals of the Pelusa area were formed under a relatively oxidizing and/or neutral pH condition, compared with other Chilean IOCG deposits. [ABSTRACT FROM AUTHOR]

Published
2023
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10. Early Jurassic arc related magmatism associated with porphyry copper mineralization at Zafranal, Southern Peru unraveled by zircon U-Pb ages

Author

Santos, Alan, Weimin, Guo, Rivera, Fernando, Tassinari, Colombo, Cerpa, Luis, and Kojima, Shoji

Subjects
Zafranal porphyry, U-Pb zircon age, Coastal Batholith, Early Jurassic, Batolito de la Costa, Jurásico temprano, Pórfido Zafranal, Edades U-Pb en circones, SHRIMP
Abstract

Early Jurassic arc-related igneous rocks host porphyry copper prospects and gold-bearing quartz vein deposits in southern Peru. Ten new zircon U-Pb ages for wall rocks of gold-bearing quartz veins, Jurassic rocks and copper-mineralized porphyry bodies in Zafranal porphyry copper, together with published ages for Jurassic rocks, reveal a continuous magmatic evolution of the early Jurassic arc. The Jurassic rocks and gold-bearing quartz vein systems in the western flank of the Western Cordillera are hosted by Paleo- and Meso-proterozoic orthogneisses of the Arequipa Massif (1.75-1.44 Ga) that underwent Grenville-age metamorphism ~1 Ga. The early mafic magmatism is recorded between 199.6-193.2 Ma, and was followed by dominantly felsic magmatism from 184.1-174.9 Ma. Both magmatic events have formed the thinnest intrusive belt (

Published
2019

13. Nature of (Ca(super 2+))(sub i) transients during ventricular fibrillation and quinidine treatment in perfused rat hearts

Author

Kojima, Shoji, Wikman-Coffelt, Joan, Wu, Shao T., and Parmley, William W.

Subjects
Quinidine -- Analysis, Ventricular fibrillation -- Research, Rats -- Anatomy, Biological sciences
Abstract

Calcium transients respond rapidly to electrical signals with maximum frequency of 19 hertz during pacing-induced ventricular fibrillation (VF) in perfused rat hearts. Quinidine addition to the heart reduces the VF rate excessively and activates all the calcium transients to respond to electrocardiogram signals. Prolonged quinidine treatment for about 20 minutes retards the functional revival of calcium transients after defibrillation due to the overloading of the transients.

Published
1994

15. Effects of perfusion pressure on intracellular calcium, energetics, and function in perfused rat hearts

Author

Kojima, Shoji, Shao T. Wu, Watters, Thomas A., Parmley, William W., and Wikman-Coffelt, Joan

Subjects
Perfusion (Physiology) -- Physiological aspects, Heart -- Contraction, Calcium ions -- Physiological aspects, Biological sciences
Abstract

The effects of perfusion pressure on intracellular Ca2+ concentration, cardiac function, energy metabolism and left ventricular geometry in perfused rat hearts were investigated. A surface fluorometry technique was used to evaluate beat-to-beat changes in Ca2+ concentration due to perfusion pressures ranging from 50 to 140 cmH2O. The results showed that perfusion pressure modulates Ca2+ concentration, which in turn regulates myocardial contraction and possibly O2 utilization.

Published
1993

19. Distribution of gold and silver and its relation with hypogene ore minerals in the Esperanza porphyry deposit, Antofagasta Region, Chile.

Author

Kojima, Shoji, San Martín, María Constanza, Nagase, Toshiro, Nakashima, Daisuke, Bisso, Claudio, and Menzies, Andrew

Subjects
*GOLD, *PORPHYRY, *ELECTRON probe microanalysis, *MINERALS, *ORES, *SILVER sulfide, *GOLD ores, *PRECIOUS metals
Abstract

Modes of occurrence of Au‐ and Ag‐bearing phases and their relation with associated hypogene ore minerals were examined with the objective to elucidate Au‐Ag distribution at the Esperanza porphyry deposit in the Eocene Centinela copper belt, using ore‐microscope modal analysis, semi‐quantitative analyses by automated mineralogy, electron probe microanalysis, and secondary ion mass spectrometer. The Esperanza hypogene mineralization is characterized by early‐stage chalcopyrite‐rich veinlets in the potassic alteration zone and later polymetallic stage with tennantite and galena in the chlorite‐sericitic alteration zone. Only the early‐stage chalcopyrite contains fine‐grained electrum (Au68Ag32 ‐ Au81Ag19) and hessite (Ag2Te), and thus yields positive correlations in Cu vs. Au and Cu vs. Ag grades that are clearly recognized in the hypogene sulfide zone. The early‐stage chalcopyrite grains frequently exhibit polysynthetic twinning suggestive of inversion from intermediate solid solution. These features suggest that the fine‐grained electrum and hessite are products exsolved in the cooling process with the intermediate solid solution to chalcopyrite inversion. In contrast, tennantite and galena of the later‐stage mineralization contain no detectable Ag, and it is thus proposed that the early‐stage inverted chalcopyrite is the principal storage of economically important precious metals. [ABSTRACT FROM AUTHOR]

Published
2021
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21. Sr- and Nd- isotope variations along the Pleistocene San Pedro – Linzor volcanic chain, N. Chile: Tracking the influence of the upper crustal Altiplano-Puna Magma Body

Author

Godoy, Benigno, primary, Wörner, Gerhard, additional, Le Roux, Petrus, additional, de Silva, Shanaka, additional, Parada, Miguel Ángel, additional, Kojima, Shoji, additional, González-Maurel, Osvaldo, additional, Morata, Diego, additional, Polanco, Edmundo, additional, and Martínez, Paula, additional

Published
2017
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23. Intracellular calcium transients underlying interval-force relationship in whole rat hearts: effects of calcium antagonists

Author

Zaugg, Christian E., Kojima, Shoji, Wu, Shao T., Wikman-Coffelt, Joan, Parmley, William W., Buser, Peter T., Zaugg, Christian E., Kojima, Shoji, Wu, Shao T., Wikman-Coffelt, Joan, Parmley, William W., and Buser, Peter T.

Abstract

Objectives: Much of the understanding about the cardiac interval-force relationship of the whole heart, including mechanical restitution and postextrasystolic potentiation (PESP), has been inferred from isolated muscle studies. We tested whether results from isolated muscles about intracellular Ca2+([Ca2+]i) transients underlying the interval-force relationship can be substantiated in whole hearts. Additionally, we investigated whether Ca2+ antagonists could alter [Ca2+]i transients underlying mechanical restitution and postextrasystolic potentiation. Methods: [Ca2+]i transients were studied in isolated perfused rat hearts by surface fluorometry and Indo-1. Using computer-controlled pacing protocols, we performed restitution curves for left ventricular developed pressure and [Ca2+]i (developed pressure and [Ca2+]i plotted as a function of extrasystolic intervals). To quantify restitution curves, we fitted monoexponential functions to plots and analyzed their shift and slope. Then, we used Ca2+ antagonists, low extracellular Ca2+([Ca2+]o) and PESP to modify restitution curves. [Ca2+]i transients in isolated rat hearts were interpreted as Ca2+ released from the sarcoplasmic reticulum. Results: Interval-dependent changes in developed pressure were strongly correlated to interval-dependent changes in the amplitude of [Ca2+]i transients in isolated whole rat hearts. Additionally, nifedipine and low [Ca2+]o led to similar downward shifts but not to a changed slope of restitution curves for [Ca2+]i. On the other hand, PESP increased the slope of restitution curves for [Ca2+]i. Furthermore, the effect of PESP on developed pressure was blunted by high concentrations of Ca2+ antagonists. Conclusions: The results from isolated muscles about [Ca2+]i transients underlying the interval-force relationship could be substantiated in whole hearts. Additionally, low [Ca2+]i (induced by nifedipine or low [Ca2+]o) decreased the maximal Ca2+ release of the sarcoplasmic reticulum but did

Published
2017

32. Comparative renal toxicity of metallothioneins with different cadmium/zinc ratios in rats

Author

Shimada Hideaki, Furukawa Akihiko, Kojima Shoji, and Kiyozumi Morio

Subjects
chemistry.chemical_element, Urine, Zinc, Toxicology, Kidney, Urinary excretion, Glycosuria, medicine, Animals, Aspartate Aminotransferases, Cadmium, Dose-Response Relationship, Drug, Renal damage, Rats, Inbred Strains, General Medicine, Molecular biology, Rats, Proteinuria, medicine.anatomical_structure, Biochemistry, chemistry, Sephadex, Toxicity, Chromatography, Gel, Metallothionein, Copper, Injections, Intraperitoneal
Abstract

The comparative renal toxicity of rats after injection of cadmium (Cd) and zinc (Zn)-metallothioneins (MTs) with different Cd Zn ratios at the same dose of 200 μg MT-bound Cd kg was studied. From determination of the urinary excretion of protein, aspartate aminotransferase (AST) and glucose, which are indices of Cd-induced renal damage, the extent of the renal toxicity of the MTs used here was in the order ( 1Cd 0Zn )-MT = ( 2Cd 1Zn )-MT > ( 1Cd 2Zn )-MT > ( 1Cd 6Zn )-MT. The characterization of Cd, Zn and Cu in the urine after injection of MTs was examined using a Sephadex G-75 column. ( 1Cd 0Zn )-MT injection showed that Cd was present mainly in lower-molecular-weight fractions, with only small amounts of Cd in the MT fraction. Upon injection of other MTs, Cd was present mainly in the MT fraction and increased with decreasing Cd Zn ratio. Zn was present mainly in lower-molecular-weight fractions and Cu mainly in the MT fraction, indicating the replacement of MT-bound Zn by Cu. The cumulative urinary excretion of Cd during 12 days after injection of MTs decreased with increasing Cd Zn ratio. The Cd content of the kidney and liver increased with increasing Cd Zn ratio. The results of this study indicate that in rats injected with MTs with different Cd Zn ratios, the renal uptake of Cd increases with increasing Cd Zn ratio, resulting in more severe renal damage.

Published
1991

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