Hypogene speleogenesis related to porphyry magmatic intrusions and its influence on subsequent karst evolution in the Peruvian high Andes

Abstract

Carbonate rocks of Cretaceous and Jurassic age are widespread in the Peruvian Andes where they host numerous magmatic intrusions and related ore deposits. Most of Peru's metal ore deposits are located at high elevations within a narrow, tectonized carbonate-rock belt extending over 2000 km in length. Many of the limestone formations are karstified and characterized by high recharge and percolation rates, well-developed subsurface drainage and complex flow patterns. Knowledge of karst in the Andes is generally limited, although karst is recognized to cause extreme hydrogeologic complexity and great challenges in development of mining facilities located in carbonate settings. Aspects of the origin of void/conduit systems (i.e. speleogenesis) and karst evolution are rarely addressed in environmental impact and risk assessment studies.This study in the Antamina area in the east side of the Cordillera Occidental, home to the world largest known skarn copper‑zinc deposit, demonstrates that the current karst system has formed as the result of polygenetic and multi-phase development. Structure-controlled hypogene cave systems are well-preserved and widespread in the area and present a foremost example of endogenous hypogene speleogenesis related to magmatic intrusions. Hypogene karst structures have strongly influenced subsequent epigene karstification, which commenced at the Pliocene-Pleistocene boundary. Changes in the base-level position due to the landscape evolution and Pleistocene glaciations were major additional factors that influenced epigene karst development. The findings of this study are potentially relevant to assessing karst origin and hydrogeology in many carbonate-hosted ore deposits in the Peruvian Andes and other regions. This study shows that the speleogenetic and evolutionary approach is indispensable in the development of sound conceptual models of groundwater flow in karst terrains and the assessment of karst-related hazards and risks.