Uneconomic epithermal precious metal mineralization and associated alteration occur in the Tonopah Property, and are similar in style, although much less intense, to the deposits of the Tonopah camp two miles south. Mineralization is localized within a set of northwest-trending faults within the Tonopah, Mizpah, and King Tonopah Member of the Fraction-Tuff formations, and is associated with widespread propylitic and sparse fracture-localized potassic and argillic alteration. A younger set of Mn-calcite veins, anomalous in manganese, mercury, arsenic, and antimony, occurs in northeast-trending faults cutting older formations as well as the younger Tonopah Summit Member of the Fraction Tuff. This mineralization is possibly associated with silicification, zeolitization, and clay-alteration of the Fraction Tuff. The Tonopah Summit Member of the Fraction Tuff is reinterpreted as younger than the King Tonopah Member. Mega-breccia and basin morphology in the northeast may indicate an eruptive vent in this area.

Submitted by CARLA MARIA GOULART DE MORAES (carlagm) on 2015-04-23T14:47:46Z No. of bitstreams: 1 Caracterizacao das rochas vulcanicas.pdf: 6912939 bytes, checksum: 658d534ba5ce96162be35ee8e9b12ce6 (MD5) / Made available in DSpace on 2015-04-23T14:47:46Z (GMT). No. of bitstreams: 1 Caracterizacao das rochas vulcanicas.pdf: 6912939 bytes, checksum: 658d534ba5ce96162be35ee8e9b12ce6 (MD5) Previous issue date: 2006 / Nenhuma / O Alvo Estrela (Cu-Au) está localizado na extremidade leste da Falha Carajás, na região da Serra do Rabo. Ele compreende uma área de 1,6 por 2,4 km, composta por andesitos, gabros e riolitos arqueanos do grupo Grão Pará, formações ferríferas da Formação Carajás, arenitos arcoseanos da Formação Gorotire e granitóides paleoproterozóicos. O minério de Cu-Au é epigenético, ocorrendo em veios brechados, stockworks, e também disseminado nos andesitos. Os riolitos, objeto de estudo deste trabalho, formam faixas em contato com andesitos a NE e a SW na área do Alvo. Eles são formados por fenocristais de oligoclásio e quartzo, imersos em uma matriz de fragmentos finos de oligoclásio alterados para Fe-biotita com posterior siderofilitização e albita substituída por sericita e quartzo. Os granitóides, também objeto de estudo, são intrusivos no pacote andesítico e compreendem quartzo diorito e álcali-feldspato granito a quartzo-álcali-feldspato sienito, englobando três fácies: albita-ortoclásio granito, episienito e topázio-albita-ortoclásio granito. O quartzo diorito é portador de fenocristais de andesina e ortoclásio transformados em albita, sericita e siderofilita, e com quartzo intersticial. O albita-ortoclásio granito é constituído por albita, feldspato potássico pertítico alterado para sericita, protolitionita e lepidolita, além de quartzo e topázio. O episienito potássico é granular e poroso. Fluorita e clorita preenchem os espaços vazios, possivelmente do quartzo dissolvido. O topázio-albita-ortoclásio granito só difere do albita-ortoclásio granito pela maior quantidade de topázio, de feldspato potássico sericitizado, de matriz e de zinnwaldita e lepidolita. As rochas félsicas e intermediárias do Alvo foram afetadas por alteração potássica precedida por albitização e seguida por greisenização. A siderofilita foi o mineral dominante na alteração potássica, bem como, protolitionita, zinnwaldita, lepidolita e topázio o foram na greisenização. Os riolitos do Alvo Estrela comparados aos da Serra Norte são mais enriquecidos em Rb, Cs, Th, U, Ta e Cu e empobrecidos em Ba. O albita-ortoclásio granito e o topázio-albita-ortoclásio granito são cálcio-alcalinos a alcalinos, sendo o primeiro ainda peraluminoso. Os valores de Ga (67,2 ppm), Nb (67,36 ppm) e Ce (67,5 ppm), assim como as razões Ga/Al2O3 (4,49) e Fe/Mg (233,25) do albita-ortoclásio granito, sugerem que ele seja quimicamente semelhante aos granitos do tipo A, tal como os granitos paleoproterozóicos de Carajás e os fanerozóicos da Austrália. A coincidência nos padrões de ETR entre os riolitos do Alvo e os da Serra Norte, e a associação andesito-riolito observada em ambos, sugere uma possível correlação com os riolitos do Grupo Grão Pará. A semelhança nos padrões de ETR entre o albita-ortoclásio granito e topázio-albita-ortoclásio granito, sugerem que este último derive de evolução metassomática do primeiro. O episienito também mostra semelhanças nos padrões de ETR comparado com o albita-ortoclásio granito, coincidindo com as fácies mais hidrotermalizadas. O padrão de ETR do tipo gaivota, a razão Lu/Ybn entre 1,01 e 1,08 e a diminuição conteúdo total dos ETR no sentido do albita-ortoclásio granito (323,08 ppm) para o topázio-albitaortoclásio granito (74,18 ppm) são compatíveis com os granitos Pojuca, Serra Branca e Pedra Branca. A semelhança da razão Fe2O3/FeO do albita-ortoclásio granito (0,01 a 0,11) e do topázio-albita-ortoclásio granito (0,08 a 0,13), sugere que ambos se equilibraram sob condições de fugacidade de oxigênio semelhantes, enquanto que o episienito (0,55 a 0,78) se equilibrou em um ambiente mais oxidado. O estudo químico das micas revelou que a greisenização ocorreu em um ambiente já em resfriamento e a pressão maior do que a alteração potássica, dada a falta de titânio nas protolitionitas e lepidolitas, e o elevado conteúdo de AlVI nessas micas e nas zinnwalditas. / The Estrela Cu-Au deposit is situated in the Serra do Rabo, at the easternmost part of Carajás shear zone, at the Serra dos Carajás region. It is hosted by altered andesites and gabbros and rhyolites of the Grão Pará Group, Itacaiunas Supergroup, formed at 2.76 Ga (Sm-Nd isochronic age) cut by Paleoproterozoic porphyritic quartz diorite, orthoclase-albite granite, topaz-orthoclase-albite granite and quartz-alkali-feldspar syenite (episyenite). The Cu-Au ore is epigenetic, mostly in quartz veins, disseminated in the host rocks, or forming the matrix of brecciated quartz veins. The rhyolites are distributed for 2.4 km along a WNW trending ridge, presenting mylonitized contacts with andesites to the SW and to the NE. They are composed of oligoclase and quartz phenocrysts in a matrix of oligoclase partially replaced by Fe-biotite and siderophyllite, and albite replaced by sericite and quartz. The orthoclasealbite granite, topaz-orthoclase-albite granite and quartz-alkali-feldspar syenite (episyenite) are different facies of the same granitoid intrusion. The quartz diorite is composed of andesine and orthoclase phenocrysts replaced by albite, sericite and siderophyllite in a matrix of the same minerals plus interstitial quartz. The orthoclase-albite granite facies is formed by albite, perthitic orthoclase replaced by sericite, protolithionite and lepidolite, together with quartz and topaz. The topaz-albite-orthoclase granite facies presents larger contents of topaz, zinnwaldite, lepidolite and sericitization of the orthoclase, compared with the orthoclasealbite granite facies. The episyenite is a granular and porous rock composed of a potassic feldspar matrix containing vugs filled with fluorite and chlorite. The felsic and intermediate rocks were affected by potassic alteration preceded by albitization and followed by greisenization. Siderophyllite dominated in the potassic alteration, whereas protolithionite, zinnwaldite, lepidolite and topaz dominated in the greisenization. The Estrela rhyolites show higher Rb, Cs, Th, U, Ta and Cu and lower Ba contents than the Serra Norte rhyolites. The albite-orthoclase granite and the topaz orthoclase granite are calk-alkaline to alkaline and peraluminous rocks. The Ga (67.2 ppm), Nb (67.36 ppm) and Ce (67.5 ppm) values, and the Ga/Al2O3 (4.49) and Fe/Mg (233.25) ratios of the albite-orthoclase granite are analogous to A-type granites, mainly to the Proterozoic Carajás Granites and to the A-type Phanerozoic Australian Granites. The association of the Estrela and Serra Norte rhyolites with Neoarchean andesites, along with the coincidence of REE patterns suggests that the Estrela rhyolites belong to the Grão Pará Group. The albite-orthoclase granite, topaz-albite-orthoclase granite and episyenite REE patterns also suggest that the last two are derived from metasomatic evolution of the first. The seagull-type REE pattern, associated to the Lu/Ybn ratio (1.01 ? 1.08) and the decreasing of total REE content from the albite-orthoclase granite (323.08 ppm) to the topazalbite granite (74.18 ppm) are analogous to the Pojuca (Carajás), Serra Branca and Pedra Branca (Goiás) granites.The Fe2O3/FeO ratios of the albite-orthoclase granite (0.01 - 0.11), topaz albiteorthoclase granite (0.08 ? 0.13) and episyenite (0.55 ? 0.78) indicate that the last equilibrated at a more oxidizing environment than the others. The almost absence of Ti in the protolithionites and lepidolites and the high content of AlVI in the protolithionites, lepidolites and zinnwaldites indicate that the greisenization took place in a cooling hydrothermal system and at higher pressure than the preceding potassic alteration.

published_or_final_version / Earth Sciences / Master / Master of Philosophy

No description available.

No description available.

A combined field and laboratory investigation of the primarily volcanic Roskruge range, Pima County, Arizona, produced the following results: The rocks in the area fall into three major and several minor divisions. The major groups are: (1) The pre-Laramide dark-colored andesites and sediments that floor the range. A K-Ar date on one of the andesites produced a number, 108 m. y. , on a whole rock analysis. (2) The brightly colored and widespread Laramide volcanics and an associated hypabyssal pluton at Cocoraque Butte, which gave K-Ar mineral ages in the 74 m. y. to 66 m. y. spread. (3) The mid-Tertiary potassic basaltic andesites found on an eroded plain that is cut into the Laramide volcanics. These dark-colored extrusives were dated at 23 m. y. by whole rock K-Ar. Amongst the minor units in distribution is the petrographically unusual Recortado ash flow, a small 13 m. ye old unit that preserves a vitrophyre just above its base. Also included in the miscellaneous group of units are the post-orogenic true basalts, which appear as dikes and as a flow(?) at Brawley Wash and which gave whole rock K-Ar dates of about 10 m. y. Initial strontium 87/86 ratios indicate that the Laramide and mid-Tertiary rocks (including the Recortado ash flow) have values ranging from . 7056 to .7092, while the Brawley Wash basalt has a true deep-seated basalt ratio of .7038. The combination of radiochemical assay, petrographic and field study, and isotopic data has established good gross correlation with the already known sequence of formations and plutons in the Tucson Mountains.

Thesis (Ph.D.)--McMaster University (Canada), 1992. / Source: Dissertation Abstracts International, Volume: 54-02, Section: B, page: 0696.

Thesis (M.S.)--University of Montana, 2008. / Title from title screen. Description based on contents viewed Aug. 26, 2008. Includes bibliographical references (p. 64-69).

Thesis (M.S.)--Oregon State University, 2006. / Printout. Includes bibliographical references (leaves 36-39). Also available on the World Wide Web.

This study lias initiated with the aim of identifying the existence of any geochemical criteria which may be used to distinguish between the various volcanic formations within the Witwatersrand triad. The Witwatersrand triad comprises three sequences: the Dominion Group at the base, the Witwatersrand Supergroup in the middle, and the Ventersdorp Supergroup at the top. It is underlain by Archaean basement rocks, and covered by rocks of the Transvaal sequence. The Dominion Group consists of the sedimentary Rhenosterspruit quartzite Formation at the base, overlain by a bimodal component of the Syferfontein Porphyry succession of lavas. Basaltic lavas are the major component of the Rhenosterhoek Formation, while the overlying Formation consists primarily of dacitic porphyries. Intercalations of one lava type within the other are common, however, so each formation is not the exclusive domain of only one lava type. The Witwatersrand Supergroup, a predominantly argillaceous and arenaceous sequence, contains two narrow volcanic horizons, one of wbich, the Jeppestown Amygdaloid (now Crown Formation), consisting of tholeiitic andesites, occurs in the study area. The overlying Ventersdorp Supergroup has, at its base, the basaltic Klipriviersberg Group, of which four out of six formations are present in the study area, namely, the Alberton, Orkney, Loraine and Edenville Formations. This group is succeeded unconformably by the PIatberg Group, consisting of the sedimentary Kameel doorns Formation, followed by the (informal) Goedgenoeg, Makwassie Quartz Porphyry and Rietgat Formations. The Goedgenoeg and Rietgat Formations are basaltic, whil e the Mawassie rocks range from basaltic to dacitic, the majority being tholeiitic andesites and andesites . The Pniel sequence at the top of the Ventersdorp Supergroup consists of the sedimentary Bothaville Formation, and the Allarridge Formation, the lavas of which are basaltic with some andesitic tendencies. A well-defined geochemical stratigraphy was found to exist. From the eleven volcanic formations examined, nine distinct geochemical units emerged, as the Loraine and Edenville Formations were found to have the same geochemical characteristics, as did the Goedgenoeg and Rietgat Formations. Despite having undergone law-grade greenschist facies metamorphism, very clear variation patterns with height are displayed by the immobile elements Ti, P, Kb, Zr and Y, and the light rare earth elements La, Ce and Nd. In contrast, much scatter was observed in the variation patterns of Na, K, Mn, Ba and Rb. Three techniques were employed to effect discrimination between formations - orthosonal discrimination, interelement and ratio vs ratio plots, and discriminant analysis. Confidence limits placed on normal probability plots served to isolate outlier samples for further examination by the various discrimination techniques. A successful test of the efficacy of the discrimination techniques was afforded when fourteen samples from an unknown succession were positively identified as representative of the Klipriviersberg Group