Session Details
Thayer Lindsley Award recipient: La Colorada Exploration Team
The potential for a skarn-type mineralized system beneath the La Colorada Mine in Zacatecas, Mexico, had been debated by Pan American Silver geologists for many years. A technical paper published in 2001 proposed the possibility of a skarn system at depth, but at the time the concept remained speculative, supported only by limited geological evidence, including the presence of calc-silicate minerals.
As mining progressed to greater depths, an exploration crosscut was developed on the 498 Level to provide access for deeper drilling. In 2018, exploration drilling primarily targeting the known vein system began intersecting mantos and carbonate replacement deposit (CRD) mineralization. These observations strengthened the geological case for a much larger mineralizing system at depth and prompted the exploration team to design a focused drilling program to test for skarn mineralization.
Only months into the program, drill hole U-39-18 intersected 222.55 metres grading 69 g/t silver,1.87% lead and 3.36% zinc. Together with subsequent drill holes, this intercept defined the first major orebody and led to the announcement of the La Colorada Skarn discovery on October 23, 2018.
Following the discovery, Pan American Silver initiated an aggressive drilling campaign beneath and adjacent to the La Colorada Mine. Step-out drilling to the west during 2019 discovered a second major orebody, substantially increasing the known scale of the mineralized system.
As geological understanding evolved, the exploration team recognized the importance of the causative intrusive body identified east of the first orebody. Testing the opposite side of this porphyry stock led to the discovery of a third major orebody in 2020, further demonstrating the scale and continuity of the system.
The success of the exploration program was driven by a continuously evolving geological model that brought together multiphase epithermal veins, CRD mineralization, silver-rich lead-zinc skarns and copper-molybdenum porphyry mineralization as components of a single, vertically extensive hydrothermal system.
Today, the La Colorada Skarn is one of the world's largest lead-zinc skarn deposits and remains open in several directions. Since its discovery, approximately 360 kilometres of drilling have been completed on the skarn target, in addition to continued exploration of the overlying epithermal vein system. This work has defined resources containing approximately 368 million ounces of silver, 4.2 million tonnes of lead and 9.2 million tonnes of zinc. The exceptional scale and tenor of the mineralization are illustrated by drill intercepts including 97 metres grading 654 g/t silver, 15.35% lead and 11.39% zinc, and 439.5 metres grading 72 g/t silver, 2.13% lead and 3.27% zinc.
What makes La Colorada particularly remarkable is the preservation of an unusually complete mineralized system. From the deeper intrusive and porphyry environment through skarn and CRD mineralization to the overlying epithermal veins, the deposit records a continuous, subvertical hydrothermal system of exceptional scale and geological preservation.
Geological evidence supports a Laramide-aged intrusive event comprising porphyries ranging from andesitic to rhyolitic composition. These intrusions generated calcic skarn and associated CRD mineralization, together with intermediate-sulfidation epithermal veins hosted within both sedimentary rocks and volcanic rocks of the Lower Volcanic Sequence. The result is a rare, remarkably complete example of a mineralizing system in which multiple deposit styles can be observed together, almost as they would be illustrated in a geology textbook.
