Summary:
The Yauricocha mine features several mineralized zones which have been emplaced along structural trends, with the mineralization itself related to replacement of limestones by hydrothermal fluids related to nearby intrusions. The mineralization varies widely in morphology from large, relatively wide, tabular manto-style deposits, to narrow, sub-vertical chimneys. The mineralization features economic grades of Ag, Cu, Pb and Zn, with local Au to a lesser degree. The majority of the mineralization is related to the regional high-angle NW-trending Yauricocha fault, or the NEtrending and less well-defined Cachi-Cachi structural trend. The mineralization generally presents as polymetallic sulfides but is locally oxidized to significant depths or related to more Cu-rich mineralization.
Goyllarisquizga Formation
The oldest rocks exposed in the area are the lower Cretaceous Goyllarisquizga arenites. This formation is approximately 300 m thick and comprises thick gray and white arenites, locally banded with carbonaceous lutites as well as small mantos of low-quality coal beds and clay. In the vicinity of Chaucha, these arenites have near their base interbedded, red lutite. The arenites crop out in the cores of the anticlines southwest of Yauricocha, as beds dispersed along the Chacras uplift, and isolated outcrops in the Éxito zone.
Jumasha Formation
The mid-Cretaceous Jumasha Formation consists of massive gray limestone, averages 700 m thick, and concordantly overlies the Goyllarisquizga Formation. Intercalations of carbonaceous lutites occur at its base near the contact with the arenites. These layers are succeeded by discontinuous lenses of maroon and grey limestone, occasionally with horizons of lutite and chert about 6 m thick. Also present are pseudo-breccias of probable sedimentary origin and a basaltic sill.
Celendín Formation
The Celendín Formation concordantly overlies the Jumasha Formation and contains finely stratified silicic lutites with intercalations of recrystallized limestone of Santoniana age as well as the France Chert. The average thickness in the Yauricocha area is 400 m.
Casapalca Red Beds
The Casapalca red beds lay concordantly on the Celendín Formation with a gradational contact. It has been assigned an age between upper Cretaceous and lower Tertiary, but because of the absence of fossils its age cannot be precisely determined. It is composed primarily of calcareous red lutites, pure limestones, and reddish arenaceous limestone. Lava flows and tuffaceous beds have been occasionally reported.
Mineralization at the Yauricocha Mine is represented by variably oxidized portions of a multiple-phase polymetallic system with at least two stages of mineralization, demonstrated by sulfide veins cutting brecciated polymetallic sulfide mineralized bodies. The mineralized bodies and quartz sulfide veins appear to be intimately related and form a very important structural/mineralogical assemblage in the Yauricocha mineral deposit. Comments made herein regarding the characteristics of the Yauricocha district apply directly to the Yauricocha Mine.
Mineralization in the Yauricocha district is spatially and genetically related to the Yauricocha stock, a composite intrusive body of granodioritic to quartz monzonitic composition that has been radiometrically dated at late Miocene (approximately 7.5 million years old) (Giletti and Day, 1968). The stock intrudes tightly folded beds of the late Cretaceous Jumasha and Celendín Formations and the overlying Casapalca Formation (latest Cretaceous and Paleocene?). Mineralized bodies are dominantly high-temperature polymetallic sulfide bodies that replaced limestone. Metal-bearing solutions of the Yauricocha magmatic-hydrothermal system were highly reactive and intensely attacked the carbonate wall rock of the Jumasha and Celendín Formations, producing the channels in which sulfides were deposited.
Production
Sierra has decided that the 5,500 tpd production rate option is the recommended case for a future pre-feasibility study. Increased production rates beyond 5,500 tpd may be possible once Yauricocha has resolved the mineralized material and waste haulage issues.
| Commodity | Units | LOM |
|
Copper
|
M lbs
| 333 |
|
Gold
|
koz
| 20 |
|
Silver
|
M oz
| 11 |
|
Zinc
|
M lbs
| 400 |
|
Lead
|
M lbs
| 131 |
All production numbers are expressed as payable metal.