Dacitic Pyroclastics Research Articles

Hydrogeological Features of Geothermal Waters in Havran (Balıkesir), Turkey

In this study, geothermal waters of Havran were studied in detail. In the area, Karakaya formation in Early Triassic age is the basement consisting volcanic and sedimentary rocks such as of basalts, mudstones, and radiolarites in which there are intercalations of limestone, sandstones and conglomerates. Granodiorite intrusions in Oligocene to Miocene age occur in association with intense volcanic events in the area. From Upper Oligocene to Early Miocene, andesitic and dacitic pyroclastics occur due to intensively volcanism in the area. Later, lacustrine sediments consisting of conglomerates, sandstones, claystones, marls and limestones form from Middle to Upper Miocene. Geothermal waters in the area of Havran are of Na-Ca-(SO4)-HCO3, Na-(SO4)-HCO3 and Na-SO4 type. The geothermal waters display immature waters and were represented within this study as a hydrogeological model.

Thermoluminescence behaviors of quartz in the Miocene dacitic pyroclastics and geothermal exploration in Tsunagi-hot springs, Morioka, Northeast Japan

Thermoluminescence behaviors of quartz in the Miocene dacitic pyroclastics and geothermal exploration in Tsunagi-hot springs, Morioka, Northeast Japan

Origin of Gypsum Formations in Copper Deposit of Murgul, NE Turkey

The Anayatak and Çakmakkaya orebodies forming the Cu deposit of Murgul in the East Pontic metallotect, NE Turkey were completed before supergene alteration and erosion occurring in short periods of time under subaerial conditions in the area. Furthermore, pyroclastics and sediments (up to 10 m) in the Cu deposit of Murgul represent the short time interval as marker bed. It is an important element for the terrestrial conditions dominated in the area. The local identifier marker bed with ore under atmospheric conditions at the surface, sedimentation dacitic pyroclastics and alteration is interpreted as the result of the erosion events. Gypsum formations located on the upper level of the formerly existing Bognari orebody refer to a brecciated bearing mineralization formed under atmospheric conditions. In this last case gypsum formations can indicate an environment by oxidation of sulfide minerals associated with atmospheric conditions, unlike some of the research results. In Çakmakkaya orebody, gypsum minerals found in altered dacitic pyroclastics are genetically different from above described gypsum minerals. The origin of gypsum minerals can be attributed to seawater sulfates reduced by Fe-oxide/-hydroxide phases. Gypsum minerals in pyroclastics of Anayatak and Çakmakkaya orebodies are not related to host rocks ore mineral assemblage and must be considered as prior to sulfide mineral assemblage. Later on, investigation area exposed to tectonic uplift and subsequent Cu deposit of Murgul formed under terrestrial conditions.

La mayor erupción pliniana del volcán Arenal, Costa Rica

Among the pyroclastic products extruded by the Arenal volcano, one of the units is clearly distinctive in terms of particle size, thickness, areal extension and distance from the vent. This unit is the result of an explosive eruption of plinian type. From tephra analysis, the volume of the dacitic pyroclastics was determined as 0.4 km3, equivalent to 0.21 km3 of dense rock. The area covered was 1000 ± 100 km2 with a thickness ranging from 2-3 m to 5 cm. Archeological studies indicate that the eruption had place by 1000 ± 200 A.D..A comparison of this eruption with one of the pelean type dating from 1968, shows that the volume of the described plinian eruption was 6 times greater. The area covered has larger extension by a factor of 25. Another comparative analysis can be related to the plinian explosion of Mount St. Helens (U.S.A.) on May 18, 1980 where the area delimited by the 20 om isopach contour was 27 times smaller than the of "Unit 20" produced by the Arenal plinian eruption.

Alteration Mineralogy and Geochemistry of the Hydrothermally Altered Rocks of the Kutlular (Sürmene) Massive Sulfide Deposit, NE Turkey

Volcanogenic massive sulfide deposits accompanying the Upper Cretaceous felsic rocks in the intra-arc rift zone of the Pontide palaeo-arc are common in the NE Turkey. One of them, the Kutlular (Sürmene, Trabzon) deposit, is an abandoned mine within the Upper Cretaceous mafic, felsic volcanics and subvolcanic rocks. Detailed mineralogical and geochemical studies indicate the presence of hydrothermal alteration zones around the Kutlular deposit; these alteration zones are represented by silicification-pyrite-illite zone, illite-silicification zone, illite/smectite-silicification zone, smectite zone accompanying kaolinite and halloysite in the dacitic pyroclastics, and additionally chlorite zone in the mafic volcanics. Lithogeochemical data indicate that the footwall dacitic rocks (Zr/Y= 1.39-16.39, La/Yb= 0.14-9.57) and hanging-wall basalts-basaltic andesites (Zr/Y= 2.13-5.65, La/Yb= 1.16-5.00) are transitional between tholeiitic and calc-alkaline in character. The trace element patterns of the rocks show considerable LILE enrichment (K, Rb and Ba) and depletion in Sr and Ti relative to N-type MORB. Chondrite-normalized REE patterns of the footwall show pronounced HREE enrichment. The Kutlular footwall and hanging wall alteration zones have several geochemical characteristics that show systematic changes with increasing proximity to ore body such as Na depletion as well as elevated alteration index (AI) and chlorite-carbonate-pyrite index (CCPI). Generally, hanging-wall mafic volcanics and footwall rocks have high CCPI (chlorite-carbonate-pyrite index) values, indicating the importance of chlorite and pyrite formation in these rocks. Calculated mass changes in the footwall dacites commonly are large, and result from major silica mass transfer (-9.11 to 99.68 g/100 g rock). Mass-change calculations indicate that CaO + Na_2O + MgO were leached from the rocks by hydrothermal solutions, whereas large amounts of hydrothermal iron were added. Hanging wall basalt and basaltic andesite shows mass changes that are generally much smaller than in the footwall.

Environmental Effects of the Acid Rains and Mine Drainage Around the Murgul VMS Copper Deposit, Eastern Pontides, Turkey

The Murgul copper deposit is located 7 km to the south of Murgul (Artvin) in the north-eastern part of Turkey and has been in modem operation since the 1940's. The deposit is hosted in dacitic pyroclastics of Upper Cretaceous and covered by acidic tufts, mudstone, micritic limestone and sandstone of Upper Cretaceous. The massive lens composed mainly of chalcopyrite and sphalerite is already mined out and the current production is from the stockwork zone within the dacitic pyroclastics. The ore is composed mainly of pyrite and chalcopyrite, and sphalerite, galena and sulphosalts to a lesser extent. There is a vertical variation in the chemistry and mineralogy of the deposit; sphalerite and galena increase towards upper levels of the deposit (Akqay and Tfiysiiz, 1998). Quartz is the main gangue mineral; baryte, sericite, gypsum, siderite and ankerite also occur in minor amounts. The stockwork zone is characterised by an intense silicic alteration grading outward into sericite and chlorite-rich zones (Schneider et al., 1988). The Murgul deposit has a reserve of 30,000,000 tons of ore grading at 0.97% Cu. Annual production is about 3 million tons of ore yielding 25000-30000 tons of Cu concentrate, 25000-30000 tons of sulphur and 10000-15000 tons of sulphuric acid (Akgay and Tfiysfiz, 1998). Karadeniz teknik Oniversitesi, Jeoloji Milk B61., 61080 Trabzon, Turkey

Diagenesis of Oligocene-Miocene Vitric Tuffs to Montmorillonite and K-Feldspar Deposits, Durango, Mexico

Montmorillonite and K-feldspar deposits of potential economic interest occur in the Late Oligocene-Miocene tuffs of the Vizcarra Formation in the state of Durango, Mexico. The two minerals were formed separately from rhyodacitic to rhyolitic pyroclastic deposits in a closed hydrologie system and diagenetically altered following two different patterns. In material deposited on dry land the glass was completely replaced by K-feldspar, and the interstices between the replaced glass bubbles and shards were filled with chalcedony, quartz, and albite. Pyroclastic material deposited in an alkaline lacustrine environment were diagenetically altered to montmorillonite, which formed the bentonitic tuffs widely exposed beneath the K-feldspar-rich tuff. These bentonitic tuffs contain as much as 85% montmorillonite plus authigenic chalcedony and quartz. Pyrogenic sanidine, quartz, and oxybiotite, coarse glass shards, and clastic grains make up about 8% of the clay-rich tuffs. The composition of the montmorillonite corresponds to the formula (Si3.88Al0.12)(Al1.41Mg0.59)O10(OH)2(Ca0.07Mg0.11,Na0.28K0.06). The montmorillonite is dioctahedral, the surface acidity is of the Lewis type, and the clay swells to one- and two-layer complexes. The cation-exchange capacity is 64 meq/100g; base exchange is Ca2+, 15; Mg2+, 20; Na+, 4.1; and K+, 1.0 meq/100 g. Its interlamellar charge is 18.6 microcoulombs/cm2. Dacitic pyroclastics were deposited later at higher elevations along the margins of the basin. Percolating solutions apparently removed a siliceous leachate from the dacitic glass and partially altered it to clinoptilolite.

Volcanic history, mineralization, and alteration of the Crandon massive sulfide deposit, Wisconsin

The early Proterozoic Crandon massive sulfide deposit occurs in a 280-km-long, east-trending greenstone belt along the southern margin of the Southern province of the Canadian Shield. The deposit is conformably contained within a sequence of subaqueous andesitic to dacitic pyroclastics, flows, and associated chemical sedimentary rocks which strike N 85 degrees W and dip 70 degrees to 90 degrees N. Regional metamorphism in the area achieved lower greenschist facies. Regional dip of the rocks is near vertical, but smaller scale or penetrative deformation features are rare.The footwall of the deposit consists of a thick sequence of andesitic tuff overlain by a series of volcanic breccias. Some of the breccias resulted from local fumarolic activity, whereas other breccias represent a complex history of phreatic and phreatomagmatic volcanism and silicification some distance from the deposit. Examination of the breccia types, distribution, and thicknesses suggests at least two source areas for the breccias. The breccias served as permeable conduits for the ore fluids, directing them laterally toward a syndepositional graben where the fluids were vented into a topographic depression on the ocean floor during a hiatus in local volcanic activity. Up to 100 m of massive sulfide consisting of laminae of pyrite and sphalerite with minor chalcopyrite, galena, quartz, chlorite, sericite, and dolomite and minor interbedded tuff, chert, argillite, sandy tuff, and dolomite were deposited.Following chemical sedimentation, hydrothermal venting continued producing crosscutting vein mineralization. Vein development is intimately linked to the distribution of breccia in the footwall. Ascending fluids continued to migrate laterally through the permeable breccia and deposited vein mineralization which plugged the original vent areas with fine-grained precipitates of silica and sulfide. Secondary porosity was created by refracturing of tuff and breccia. Vein mineralization, localized in the footwall of the massive sulfides, exhibits a systematic compositional variation with time and space from west to east. Beneath the west end of the deposit the earliest veins consist of quartz and grade eastward into quartz-chalcopyrite-pyrite, quartz-pyrite-sphalerite-chalcopyrite, pyrite-sphalerite, and finally pyrite veins. The distribution and degree of veining suggests two source areas which correspond to the two source areas for the lithic breccias.Recoverable reserves in the deposit are estimated at 61 million metric tons averaging 1.1 percent Cu, 5.6 percent Zn, 0.5 percent Pb, 37 g/metric ton Ag, and 1.0 g/metric ton Au.Alteration of the footwall rocks at Crandon consists primarily of silicification, sericitization, pyritization, and minor chloritization. Interaction of ore fluid with wall rock has resulted in enrichment in SiO 2 , Fe, K, F, S, Cu, Zn, As, Sb, Ba, Au, Hg, Pb, Bi, Se, and Cd and depletion in Al, Mg, Ca, Na, V, and Sr. The morphology of the alteration zone at Crandon is tabular, due to control by primary and secondary porosity.