Controles de mineralización de alta ley de Oro en la zona de sulfuros del depósito Chaquicocha, Cajamarca - Perú

Abstract

The deposits of the Yanacocha Mining District have developed a high sulphidation epithermal system and are housed in a north-northwest Miocene - Pliocene volcanic complex and extends into southern Ecuador. Chaquicocha is one of the gold deposits of the Yanacocha Mining District, with an average gold grade 5 g/t and copper grade 0.3 %. Lithologically, in depositional sequence, consists of interbedded andesitic porphyritic rocks and pyroclastic flows (unit LA), then goes to a level of fine tuff (unit Tft), crystal-rich tuffs (unit Teut), and lithic crystal tuffs (unit Ult); finally developed domes and andesitic flows (unit Upha). The whole volcanic column was cut by phreatic and hydrothermal breccia structures. Alteration in Chaquicocha deposit is typical of other high-sulfidation deposits in the district, the most important alteration is massive silica alteration because it is closely related to the mineralization of high grade gold and hosts the gold resource of Chaquicocha Sulfides; vuggy and granular silica alterations are associated with moderate to low gold mineralization and oxide zone. The intermediate argillic alteration is the limit of the mineralization. The high-grade gold in Chaquicocha Sulphides is possibly due to the multiple generations of pyrite, luzonita/enargite and covellite. Gold is commonly sub-microscopic, encapsulated in pyrite, enargite, luzonita and sulfur. In Chaquicocha deposit, faults have three main directions: NNW, NE and EW, but is interpreted that Chaquicocha structural control is NNW (Nelson, 2010), however EW control is also important in the deposit because location and distribution of hydrothermal breccias are controlled by the intersection of NNW faults with NE and EW . The high-grade gold mineralization in Chaquicocha is related to a number of geological factors: lithology, structural, alteration and mineralization. Major ore bodies rest on the bottom of the unit Teut, where crystal-rich tuffs have been replaced mainly by massive silica alteration and hosts the high-grade gold. In the bottom of the unit Teut, the hydrothermal breccias have developed favorably and host 75% of the high-grade gold mineralization. These hydrothermal breccias and high-grade gold are controlled by major structures and their intersections. NNW faults (called “The Champa”) controlled gold mineralization, but the bodies with high grade gold are located at the intersection of NNW and EW faults (called “Paty”). Mineralogically, high-grade gold is associated with the presence of covellite (primary), and to a lesser extent with pyrite, enargite, luzonita, cream silica , barite and native sulfur .