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DRILLING UNDERGROUND

In underground mines like Milpillas, specialized long-hole drill equipment was paramount for preparing rock for blasting. These powerful drills created deep, precise boreholes into which explosives were loaded. This allowed for controlled detonation, breaking up the ore body into manageable sizes for extraction, a crucial step in the mine’s production cycle.

On a daily basis, miners navigated a subterranean world where the primary target was high-grade Chalcocite, a crucial Copper sulfide ore found within the mine’s extensive enriched blankets. However, earlier operations, before the sulphide zone was reached, brought them face-to-face with a stunning array of secondary Copper minerals, particularly prevalent in the shallower, oxidized zones of the deposit. These encounters routinely included the visually striking blue Azurite and its verdant counterpart, Malachite, which often display intricate intergrowths or even pseudomorphic transformations. Furthermore, the miners commonly observed the lustrous red Cuprite and deposits of glimmering native Copper. While less frequent, other notable green Copper minerals such as Brochantite and the distinctive blue-green Chrysocolla might also be present, alongside occasional rare silicates, painting a vivid picture of the mine’s diverse mineral composition. The mine was well-known for producing exceptionally well-crystallized Volborthite, a rare Copper poly-vanadate, sometimes found on a matrix of Dickite or associated with Azurite and Malachite.
The photographs also highlight the relative scarcity of significant ‘collector-quality’ mineralized pockets conducive to specimen collecting. The Milpillas Mine, despite its economic prowess as a Copper producer, wasn’t uniformly “mineralogically rich” in the way some mineral collectors often dream. While extensive zones yielded abundant Copper ore, the frequent discovery of collector-quality Azurite and Malachite vugs, brimming with “splendent” crystals, was not an everyday occurrence. Like many commercial mining operations, Milpillas had its hot spots; certain areas provided significant quantities of high-grade Copper ore for the electrolytic plant, while others, some distinct from the primary ore body, provided treasure troves for exceptional mineral specimens. This dichotomy is a common reality in the world of mineral collecting, where the pursuit of stunning crystals often means sifting through vast amounts of economically viable yet aesthetically uninteresting ore.

When routine mining operations intersected mineralized veins and vugs, some large, containing exceptional Azurite and Malachite crystals, these occurrences were opportunistically exploited by ‘some workers’ as a means of illicit income supplementation. Penoles, the owners and operators of the mine, actively discouraged such unauthorized extraction, enforcing a strict policy of dismissal and potential criminal prosecution for apprehended individuals. Furthermore, any worker implicated in such illicit activities faced industry-wide blacklisting, effectively precluding future employment within the mining sector.

Initially, the value of these surreptitiously acquired specimens was nominal, commanding only a few pesos. However, the Internet facilitated a rapid increase in market awareness among the miners, who quickly discerned the substantial value placed on these “colored rocks” by International, particularly North American, dealers and collectors.

A NOTE ON “THIS-OR-THAT POCKET” NOMENCLATURE

The use of the term “pocket” to describe certain Milpillas mineral specimens, particularly in reference to their extraction point, transcends simple geographical identification. These labels, rather than being intrinsic descriptors understood by those who extracted the specimens, were often marketing tools designed to imbue the minerals with a specific allure. Those intimately familiar with the mine’s day-to-day operations understood that such terms were colloquialisms, not reflections of actual geological structures or mining methodology.

While official company documents certainly highlighted and celebrated areas with significant mineralization — often featuring stunning, perfectly formed crystals of Azurite, Malachite, and other Copper minerals — they deliberately avoided calling these spots “pockets.” Instead, they used more formal geological terms. Their descriptions focused on the geological structures controlling the mineralization, the types of rocks surrounding the minerals, and their exact mineral makeup. This intentional choice of language pointed to a clear difference between the casual, on-the-ground language used by some of the mine workers who opportunistically and illegally exploited the mineralized zones for personal profit and the precise, scientific terminology preferred in corporate and geological reports. It was likely an effort to keep all official communications consistent and scientifically accurate, ensuring a formal narrative throughout.

Original photos courtesy of Gonzåléz Sånchez (Author: silvia)