Latite

Abstract: During the lower and middle Miocene the western Anatolia and the eastern Aegean Sea were dominated by a calcalkaline volcanism associated with minor acid and basic volcanics. The basic subcrustal volcanics consist mainly of alkali basalts and hawaiites (9.7–11.9 m.y.), nepheline hawaiites and nepheline trachyandesites (Kula area from 1.1 m.y. to the recent times). The rhyolitic volcanics (12.5 m.y.) derived by a partial melting process in the upper crust (87Sr/86Sr=0.7121). The calcalkaline suite (16.2–21.5 m.y., mean value87Sr/86Sr=0.708) shows a trend from latite-andesites to dacites and rhyodacites; a latite andesite system related to a sinking slab of lithosphere and constituted by a mixing of oceanic crust (tholeiite), oceanic sediments and/or tectonic fragments of sialic crust is envisaged.

Abstract: This paper reports the existence of abundant magmatic sulfides in INTRODUCTION latite lava vitrophyres and vent-facies dikes from the Bingham and The eruption of sulfur-rich magmas from El Chichon Tintic districts in central Utah. These dikes and flows appear to (Luhr et al., 1984) and Mt Pinatubo (Westrich & Gerlach, be comagmatic with the ore-related monzonite intrusions. In addition, 1992) in recent years has attracted attention to the limited analytical data suggest that the magmatic sulfides contain most of solubility of sulfur in intermediate magmas and the factors the Cu and Ag present in the latites. Magmatic sulfides are preserved potentially responsible for the formation of magmatic only in the least oxidized and least degassed lavas and vitrophyres. sulfides and anhydrite. However, the occurrence of magPetrography of comagmatic dikes and intrusions suggests that matic sulfides in intermediate magmas is not universal; resorption and oxidation (S-degassing) of the globules may make many volcanic suites appear to be sulfide unsaturated. the metal content available to a magmatic ore-fluid. Minette and Inasmuch as magmatic sulfides may sequester chalcophile shoshonite lavas occur in subordinate amounts in the latitic volcanic metals, what would their presence signify in magmatic fields associated with latite–monzonite intrusions and hydrothermal systems that formed porphyry Cu and mesothermal vein ore deposits of the Tintic (Ag–Pb–Zn–Cu–Au) and Bingham deposits? Do they sequester a significant portion of the (porphyry Cu–Au–Mo) districts, Utah. The ages, chemical and magmatic Cu, Pb, Zn, Ag, and Au, thereby restricting modal compositions, and field relations of the mafic alkaline lavas metal availability of subsequent ore-forming fluids? suggest that such magmas mixed and fractionated at shallow crustal We have examined the volcanic rocks from the Tintic levels to form the ore-related latites and monzonites. The unaltered and Bingham mining districts (Fig. 1), Utah, and found mafic alkaline lavas in these districts are some of the most Cu-rich that almost all of the volcanic units contain magmatic lavas in the Great Basin province. sulfides. Some quenched dikes and intrusion margins also have preserved magmatic sulfides comparable with those in the volcanic rocks. Several lines of evidence indicate that the volcanic and intrusive rocks are comagmatic (Keith et al., 1989, 1991; Waite, 1996). The Tintic district and East Tintic sub-district in Utah have recorded over

Abstract: Detailed geochemical and field data for the volcanic sequence and intrusions of the Etendeka Igneous Province are used to construct a stratigraphic framework for petrogenetic interpretation of the evolution of the Etendeka-Parana continental flood volcanic event. Geochemical and petrographic characterization of over 1,000 analyzed samples allows 8 mafic and 17 silicic magma types to be recognized. Both silicic and mafic types can be grouped into high-Ti and low-Ti suites on the basis of elevated Ti relative to other elements. The mafic magmas are: Khumib (high-Ti), Tafelberg, Kuidas, Horingbaai, Huab, Tafelkop, Albin, and Esmeralda (all low-Ti). Amongst the silicic types, the Goboboseb, Springbok, Wereldsend, Grootberg, and Beacon low-Ti quartz latites, and the Nil Desperandum high-Ti latite have been described previously. In addition, the Hoas (low-Ti), Nadas, Sechomib, and Hoarusib, (all high-Ti) latites and the Fria (low-Ti), Sarusas, Ventura, Khoraseb, Naude, and Elliott (all high-Ti) quartz latites are described for the first time here. There is a marked provinciality in the distribution of the high- and low-Ti suites, with the former concentrated in the Northern Etendeka region and the latter dominant in the Southern Etendeka. Stratigraphic distribution of magma types allows two new formations to be defined in the Northern Etendeka – the Khumib Formation of basaltic flows and the Skeleton Coast Formation dominated by silicic sheets. The geochemical provinciality hampers precise correlations between Northern and Southern Etendeka. Available evidence suggests that the lower part of the Awahab Formation in the Southern Etendeka is coeval with the lower part of the Khumib Formation and that the silicic units in the upper part of the Tafelberg Formation probably correlate with the Skeleton Coast Formation. The paucity of Khumib dykes in relation to Tafelberg dykes and their field relationships with regard to the volcanic sequence in the Northern Etendeka suggests that the main Khumib eruptive centers lay further north, consistent with southward thinning of the Khumib basalts. In the Southern Etendeka, the Doros complex is the eruptive center of the plume-derived Tafelkop basalts, which probably built a shield volcano within the regional flood lava field. This work indicates that the Etendeka has a greater variety of both silicic and low-Ti mafic magma types than are known from the SE Parana. Detailed comparisons reveal that all the important silicic types in the Parana have geochemical equivalents in the Etendeka. New correlations are Santa Maria=Fria, Ourinhos=Khoraseb, Guarapuava=Sarusas, thus extending the previously recognized correlations between Southern Etendeka quartz latites and the Caixas do Sul and Anita Garibaldi "rhyolites." These correlations emphasize that very large volume silicic systems develop with pronounced lithospheric rifting in continental flood basalt provinces.

Abstract: Textures of hydrothermal quartz revealed by cathodoluminescence using a scanning electron microscope (SEM-CL) refl ect the physical and chemical environment of quartz formation. Variations in intensity of SEM-CL can be used to distinguish among quartz from superimposed mineralization events in a single vein. In this study, we present a technique to quantify the cathodoluminescent intensity of quartz within individual and among multiple samples to relate luminescence intensity to specific mineralizing events. This technique has been applied to plutonic quartz and three generations of hydrothermal veins at the porphyry copper deposit in Butte, Montana. Analyzed veins include early quartz-molybdenite veins with potassic alteration, pyrite-quartz veins with sericitic alteration, and Main Stage veins with intense sericitic alteration. CL intensity of quartz is diagnostic of each mineralizing event and can be used to fingerprint quartz and its fluid inclusions, isotopes, trace elements, etc., from specific mineralizing episodes. Furthermore, CL intensity increases proportional to temperature of quartz formation, such that plutonic quartz from the Butte quartz monzonite (BQM) that crystallized at temperatures near 750 °C luminesces with the highest intensity, whereas quartz that precipitated at ~250 °C in Main Stage veins luminesces with the least intensity Trace-element analyses via electron microprobe and laser ablation-ICP-MS indicate that plutonic quartz and each generation of hydrothermal quartz from Butte is dominated by characteristic trace amounts of Al, P, Ti, and Fe. Thus, in addition to CL intensity, each generation of quartz can be distinguished based on its unique trace-element content. Aluminum is generally the most abundant element in all generations of quartz, typically between 50 and 200 ppm, but low-temperature, Main Stage quartz containing 400 to 3600 ppm Al is enriched by an order of magnitude relative to all other quartz generations. Phosphorous is present in abundances between 25 and 75 ppm, and P concentrations in quartz show little variation among quartz generations. Iron is the least abundant of these elements in most quartz types and is slightly enriched in CL-dark quartz in pyrite-quartz veins with sericitic alteration. Titanium is directly correlated with both temperature of quartz precipitation, and intensity of quartz luminescence, such that BQM quartz contains hundreds of ppm Ti, whereas Main Stage quartz contains less than 10 ppm Ti. Our results suggest that Ti concentration in quartz is controlled by temperature of quartz precipitation and that increased Ti concentrations in quartz may be responsible for increased CL intensities.