IL DEPOSITO PORPHYRY-MO DI EL CRESTON (SONORA, MESSICO): RILEVAMENTO GEOLOGICO-PETROGRAFICO ED EVOLUZIONE IDROTERMALE DEL SETTORE SETTENTRIONALE

This thesis work, done in collaboration and with the support of the Canadian mining company Creston Moly Corp., is focused on exploration of the surrounding porphyry molybdenum type deposit El Creston (State of Sonora, northwestern Mexico), with the aim of increasing the degree of knowledge geological and petrographic data about the presence and distribution of mineralized zones. This work is based on the spot, on geological data, on a subsequent laboratory analysis of samples collected, and on a thorough literature search. During the fieldwork (September-December 2007) was made a geological mapping conducted at 1:5000 scale in an area of about 40 km2, with the production of two maps (geo-referentiated): a geological map at 1:10000 scale and a map of the alterations at the scale 1:15000. It was made a petrographic study, in transmitted and reflected light, for a characterization of outcrop litologies, with particular attention to alteration assemblages and their relationship. The most representative samples were analyzed in electron microscopy SEM EDS, to derive microanalytical data. The deposit is a southeastern continuation of the mineralized province of western North American Cordillera and is involved in three major units: 1) a Proterozoic basement, consisting of various ortogneiss the" Creston metagranite" (which compared to the past has been divided into four facies), the tonalitic masses, micrographic granite and Paleozoic quartzite 2) many laramidiche magmatic intrusions (80-40 Ma), which include granites, porphyritic granites, quartzmonzonites and microgranites 3) late- to post-Laramidic (<40mA) magmatic products, represented by rhyolites and diorites. Have been recognized six main hydrothermal alteration assemblages, usually linked to different types of veins: an initial Ab + Or ± Bt ± Ms alteration, not associated with veins, probably related to late magmatic transformations and a subsequent Qtz + Kfs ±Ab + Bt ± Zrn ± Py alteration, which develops mainly within the Creston metagranite and is coeval with a Qtz + Ab + Bt + Ep + Cal alteration in the dioritic rocks. These two facies of alteration are closely associated with veins , respectively Qtz + Kfs + Mo ± Ms and Qtz + Kfs + Py ± Mo; follows a Mag + Bt ± Ms ± Ep ± Zrn alteration characterized by a wide distribution area, a fourth Chl + Ep + TTN + Mag ± Cal alteration, located in remote areas and of little interest, a final Qtz + Ms / Ser + Py ± ccp ± Rt alteration, covering areas generally narrow and isolated and is connected to a vein Qtz + Ms / Ser + Py + Ccp. Through this thesis has been recognized as an extension of the Mo mineralization in the northernmost areas of the deposit, only before assumed. Mineralization only form molybdenite (MOS2), which occurs in a vein, disseminated, and as a coating along fractures / faults, was found mainly in the Creston metagranite affected by overlapping Qtz + Ab + Bt ± KFS ± Zrn alteration and Py + Mag ± Bt ± Ms ± Ep ± Zrn; strong concentrations, but extremely localized, even use of molybdenum in dioritic rocks along veins, with Qtz + Ab + Bt + Ep + Cal alteration; minor amounts of molybdenum were observed in equilibrium with the Qtz + Ms / Ser + Py ± ccp ± Rt alteration assemblages. It was recognized in directing a systematic hydrothermal mineralized veins, which are generally NW-SE direction. Faults and fractures may have had a direct structural control on mineralization Paleocene-Eocene, but a more important role they played in the restructuring of the warehouse during the Miocene, fostering the exposure of some altered and mineralized areas.