Abstract
The Mariquita porphyry Cu and Lucy Cu–Mo deposits are located in the western section of the Cananea porphyry copper district in northwestern Mexico. Four hydrothermal stages are found in Mariquita: stage I is composed of quartz–pyrite–biotite–magnetite; stage II corresponds to orthoclase–quartz; stage III consists of unidirectional veinlets of quartz–pyrite–chalcopyrite–magnetite and minor molybdenite; and stage IV consists of alunite veinlets. The Lucy deposit is characterized by only one stage and consists of quartz–molybdenite–chalcopyrite.The temperatures and emplacement depths of the mineralization in Mariquita is 1 to 1.2km and 430 to 380°C, respectively. In contrast, the mineralization in the Lucy deposit shows deeper emplacement depths (~3km) and higher mineralization temperatures (550–500°C). The sulfur isotope range (−4.6 to 3.8‰) indicates that the source of sulfur for both deposits is clearly magmatic. The δ34S values (1 to 2.5‰) from alunites from stage IV in Mariquita are the result of oxidation of sulfides from previous hydrothermal stages. The oxygen and hydrogen isotope compositions of the ore fluids involved during the mineralization of hydrothermal stages I to III in Mariquita indicate a magmatic origin, whereas the stage IV fluid involved mixing between magmatic and meteoric water components. The oxygen isotope data of the ore fluids from the Lucy deposit also suggests a magmatic origin.The new U–Pb zircon analysis, using laser ablation multi-collector ICP-MS, from the granodiorite rock that hosts Lucy deposit gives an age of 63.8±1.1Ma. The new U–Pb ages of zircons reported for two mineralizing quartz feldspathic porphyries in Mariquita yield crystallization ages of 60.4±1.1Ma and 62.7±1.3Ma. The magmatic-mineralizing pulses reported for the western portion of Cananea district increase the potential for the presence of undiscovered mineralized bodies either emplaced within the Cuitaca granodiorite (e.g. Lucy), or within the Laramide volcanic rocks. The geology and geochronology reported here contribute to a better understanding of the western and northwestern sections of the Cananea district.
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