Drive southwest from Silver City and the Burro Mountains rise as a broad, dry-looking mass rather than a single dramatic peak. The Tyrone mine has altered part of that landscape so extensively that it can seem as if copper mining created the district whole. In fact, a long sequence lies under the present form: Indigenous turquoise workings, nineteenth-century copper ventures, underground operations, experiments with leaching, and the large open-pit mine that began in the late 1960s. The metal was present throughout. The ability to profit from different parts of the deposit changed with machinery, chemistry, price, ownership, and knowledge of the rock.
The New Mexico Bureau of Geology’s Tyrone tour calls this the state’s second-largest porphyry copper deposit and places it roughly ten miles southwest of Silver City. Its extensive geological explanation is especially useful because Tyrone is not just a hole dug into a copper-colored hill. The deposit formed through a series of ancient events, then was altered again by water and weathering. A state mining survey by Elliot Gillerman describes the older Burro Mountains workings and mineral belts. Read together, these sources show why mines appeared at different times and why one district name contains several distinct industries.
An old landscape with a younger ore body
The underlying Burro Mountains include rocks more than a billion years old. The Bureau describes metamorphic rocks and granitic intrusions that record very old episodes of burial, heat, and mountain building. The Tyrone copper system itself is much younger. It is associated with a quartz-monzonite porphyry stock dated to about 53–57 million years ago. Hot fluids moved through fractures in and around that intrusion and deposited copper-bearing minerals. Even that was not the end of the story. Later uplift, erosion, oxygen, and groundwater shifted copper into richer near-surface zones. The mine operates in a rock history assembled over vastly different timescales.
A porphyry deposit is broad and generally lower in average grade than the idealized narrow vein. That broadness can make it valuable when a company can move and process enormous volumes. Mineralizing fluid traveled through networks of fractures, so the ore did not arrive in one simple sheet. The Bureau notes northeast-striking structures as important controls in Tyrone. Then weathering dissolved copper from some places and redeposited it elsewhere, a process geologists call supergene enrichment. Chalcocite and, to a lesser extent, covellite formed in an enriched zone. Still later tilting exposed part of the system to another round of oxidation, making chrysocolla and other oxidized copper minerals visible. The mountain’s mineral colors are the surface expression of several stages, not a direct map of present ore grade.
The Bureau assigns one enrichment phase to about 44–47 million years ago and another to roughly 19 million years ago. Exact geological dates are estimates from particular studies, but their separation matters. The copper did not simply crystallize once and wait unchanged for a miner. Groundwater and tectonic movement remodeled it. An early miner following a visible, richer zone could be successful without knowing the full geometry. A later company using drill holes and large-scale extraction could evaluate portions that would have been impossible to judge from a shaft. The geology explains the change in mining methods as much as the machines do.
Before the modern pit
Turquoise mining provides the district’s oldest known human mineral story. The Bureau tour reports Native mining in the area around 600 CE. Old workings and stone tools described in state turquoise research reinforce the point that nineteenth-century claimants entered a known mineral landscape. Turquoise and copper are chemically connected but historically different commodities. The blue stone was valued and worked long before companies could handle the vast copper body. The Azure mine and Elizabeth pocket story follows that gem history and a later Salars family lease in detail.
Copper underground mining was established in the early 1860s according to the Bureau tour. A shaft or tunnel made sense when workers could follow a higher-grade part of the deposit without removing the entire surface above it. Claims and companies changed over the decades. A state metal-resource review records Phelps Dodge buying the Burro Mountain Copper Company property at Leopold in 1905 and acquiring Chemung Copper Company property at Tyrone in 1912. Those dates are corporate milestones, not the first copper discovery. They show a consolidation of ground and control before the modern pit.
Leopold and Tyrone are important historical place names, but they can be confusing on a present map. Mine development, townsite changes, and later earthmoving altered the setting. A reader should not assume a historic mine named near Leopold is the same opening as a modern pit bench or an Azure turquoise working. Old reports may refer to a property group, a camp, or a particular shaft depending on the author. The spatial relationships need original maps and dates. Treat the names as evidence to organize, not as proof that one visible feature has remained unchanged.
The state review says the Burro Mountains mine was idle from 1921 until preparation for underground leaching in 1941. That pause and return are revealing. A deposit can be known but not economical under a particular cost or method. Underground leaching sought to dissolve and recover copper from material in place or from mine workings instead of extracting and concentrating all the rock conventionally. The chemistry, control of solutions, and recovery were technical problems, not a magical way to turn any low-grade rock into profit. The experiment demonstrates how miners reexamined an older deposit when their tools changed.
That gap also warns against reading a mine name as a continuous payroll. A company might hold claims, maintain equipment, study an ore body, or move a small crew while a production summary calls the property idle. Conversely, a report about active copper mining may summarize several workings under one district heading. The Leopold purchase in 1905, the Chemung acquisition in 1912, the 1921–41 lull, and the later pit opening are different kinds of milestones. A purchase did not itself remove ore; preparation for leaching did not prove profitable long-term recovery; opening a pit did not mean every proposed bench was immediately mined. Keeping each event in its proper category makes the history more accurate and more human. For workers and their families, the difference between a development project and a producing mine could determine whether there was steady work that season.
The pit era
The Bureau tour dates open-pit stripping at Tyrone to 1968; a 1986 mineral symposium abstract uses 1967 for the opening of the pit. Those dates probably refer to different steps in starting the operation. The substantive change is clear: from the late 1960s onward, large-scale surface mining became the district’s dominant form. Instead of reaching selected underground zones through relatively narrow openings, operators moved overburden and waste rock to expose a broad mineralized system. Roads, benches, processing sites, and waste facilities spread across the landscape.
The open pit did not make the earlier underground work irrelevant. Historic shafts and adits had revealed parts of the system, while twentieth-century drilling defined a more comprehensive ore body. At the same time, the pit could overprint or destroy physical evidence of older workings. A mine historian may have detailed descriptions of an Azure or copper shaft that can no longer be checked in place. This is one reason old engineering plans, claim plats, and photographs matter so much. The current landscape is a later version of the district, not a timeless view of its beginnings.
Tyrone became part of Freeport-McMoRan in 2007, according to the Bureau tour. For present operation details, consult the operator’s current North America page and state permits rather than treating an older geological publication as a live production report. The mine’s operating status, output, reserve estimate, and reclamation schedule can change. The geology in the older work remains useful; its corporate facts belong to their dates. A good history separates those two kinds of information.
Copper from rock to product
An open-pit copper operation begins long before a truck enters a bench. Geologists and engineers drill and assay rock, model the deposit, and decide which material can be mined and processed at an acceptable cost. Blast design, hauling, crushing, recovery, and waste placement then depend on that model. Ore and waste are economic categories tied to a mine plan, not simple colors. Rock with visible blue or green copper minerals can be too sparse, too contaminated, or too difficult to process; rock that looks plain can carry measurable metal. The company makes decisions from samples and engineering across thousands of tons.
Different Tyrone minerals suggest different recovery approaches. Oxidized copper minerals may be amenable to leaching, while sulfide minerals often require concentration or other treatment. The exact operating flow sheet depends on the period and the mine’s current plan. The historical mention of underground leaching in 1941 should not be mistaken for a description of every modern processing facility. Nor should “leaching” be imagined as water casually poured onto a hillside. Industrial recovery requires controlled solutions, collection systems, monitoring, and permits. A public article can explain the concept without offering unsupported claims about specific current equipment.
The pit’s waste piles and reclamation work are part of the same system. The Bureau tour includes a photograph of partial reclamation on a waste-rock pile. Regrading and vegetation can change a slope’s appearance, but a photograph alone cannot demonstrate completion or environmental performance. Mine permits and monitoring records set enforceable requirements. A reader should ask how water moves through the site, how waste is characterized, what long-term maintenance is planned, and what current agency documents say. Those are concrete questions raised by any large open pit in a dry region.
Reclamation is itself a long sequence rather than a single final photograph. Some slopes can be reshaped and seeded while extraction continues elsewhere. Vegetation has to establish under local rainfall, wind, and soil conditions; a green appearance in one season may not show whether plants will persist. Drainage controls must perform during unusual storms as well as ordinary weather. Waste rock has to be considered for its chemistry, not merely its visual roughness. These concerns are general to large copper mines, not a finding that Tyrone has failed or met any particular standard. Current permits and inspection reports are the evidence for site-specific conclusions. The historic reports used for this article were written to explain geology and production, so they cannot substitute for modern environmental monitoring.
Tyrone and its neighbors
Grant County has several well-known copper operations, and their names often merge in casual conversation. Santa Rita–Chino lies to the east, across the Silver City region, and is the state’s largest porphyry copper deposit in the Bureau account. Tyrone is the second-largest porphyry in that account. Cobre/Continental is associated with Fierro in the Central district, with a different deposit setting and mining history. All three belong to a regional copper economy, but numbers from one should never be assigned to another. The fact that the same company may have controlled several properties at a given time does not erase their separate geology.
Tyrone is also near smaller Burro Mountains histories that are not extensions of its copper body. Gold Gulch concerns worked gold-bearing gravel and an incompletely identified source. Black Hawk and Alhambra are known for unusual silver-bearing veins with nickel-cobalt minerals. The Malone district contains its own mixed mineral record. A broad mountain label is useful for orientation, but it cannot stand in for deposit-level research. These differences make the range more interesting than a single “copper mountain” story would.
The historical turquoise relationship is distinctive. The same area that held a major copper system also supported the Azure, Parker, and Porterfield turquoise workings. Some turquoise occurs where copper-bearing solutions interacted with altered, fractured rock near the surface. Yet it would be wrong to say a copper pit must contain marketable turquoise everywhere, or that any stone from a waste pile is legally available. The gem mines occupied particular zones and had their own owners and workers. Randy Salars’s 1970s family account places Calvin Salars, Ken Kostenbader, Kenny Kostenbader, and Randy at a short lease at Azure’s Elizabeth pocket. The geological literature confirms the pocket’s identity; the lease episode remains a family account awaiting records. It adds a human chapter to Tyrone without turning this copper article into the turquoise article.
What the road can teach
A traveler on public roads near Tyrone can see how the industrial landscape fits the Burro Mountains. Follow posted rules and stop only at legal, safe viewpoints. The active mine, pits, shafts, haul roads, and waste areas are not public collecting sites. The Grant County Adventure Guide’s southwestern route places Tyrone among nearby mountain and district histories without promising mine access. From a distant view, look for the contrast between undisturbed ridges and engineered slopes. It is a lesson in scale: the copper deposit and its waste movement required infrastructure far beyond a lone prospector’s tools.
The road also invites a more subtle comparison. An early underground miner needed a manageable path to a promising exposure or shaft. The open-pit company needed a reliable road network for enormous trucks, a processing system, and long-term control of land and water. These are different answers to the same geological setting. The surface that a visitor sees today records the later answer most vividly, so historical documents are needed to recover the earlier ones. A district is not just its present shape.
Do not attempt to locate an old turquoise or copper opening from the highway and treat it as abandoned. Mine maps can be inaccurate at the scale of a modern turnoff, as Gillerman noted for one mislabeled Azure location. An old working may also be inside active property, hidden by earthmoving, or dangerously unstable. Mineral rights and surface access require separate checks, and industrial land has specific restrictions. The BLM Mineral & Land Records System helps research claims on federal land but does not authorize entry into the Tyrone operation. A sound field visit may consist entirely of publicly accessible interpretation and careful reading afterward.
A district made by repeated decisions
The Tyrone story is a sequence of choices against a changing understanding of the same mineral system. Indigenous people valued turquoise. Nineteenth-century miners followed visible copper and turquoise occurrences. Companies consolidated claims and tried underground approaches. In 1941, operators prepared to revisit older workings with leaching. The late-1960s pit changed the scale and surface. Later owners continued to manage production and reclamation. Each stage was enabled by technology and constrained by costs, law, labor, and the rock’s actual mineral content.
That sequence is more revealing than asking whether Tyrone is “mined out” or where a small prospector should dig. The first question cannot be answered from a public road because reserves and mine plans change; the second misunderstands the nature of an active industrial deposit. The worthwhile questions concern the past and its evidence. Why did some zones interest underground miners? What did supergene enrichment add to the original porphyry system? How did large-scale surface mining alter older workings and neighboring communities? How do reclamation plans address the land that mining reshaped? Geological reports, historic company records, and current agency documents each answer a different part.
The Burro Mountains reward that layered reading. Their ancient rocks held a much younger copper system; weathering improved some of its ore; turquoise formed in particular altered fractures; people pursued different minerals across many generations. The pit is the most visible result, but it is not the beginning or the end of the district’s meaning. Tyrone belongs to a regional history of copper while remaining its own place, with its own geology, towns, mine methods, and family memories.
Those details deserve to be kept attached to their dates.
One practical way to keep those layers clear is to put three dated maps side by side: a pre-pit mine and town map, a late twentieth-century pit plan, and a current land-management map. Mark which document actually locates an old shaft and which merely repeats a place name. The differences can show why a remembered mine appears to have moved or vanished when viewed through a modern search result. They also make visible how much of the old landscape was transformed. This comparison is historical work, not a collecting itinerary; exact access rules still belong to the present operator and land manager.
The exercise can begin with a single question: what did the writer mean by “Tyrone”? In one document it may be a mining district; in another, a townsite; in another, a corporate property or a particular copper pit. The same ambiguity surrounds “Burro Mountains,” which can describe a range, a turquoise area, or a broad set of mining districts. Write the source’s date and geographic scope beside every figure before comparing it with another. Otherwise a production total for a company can be mistaken for one shaft, or a turquoise mine name can be plotted on a copper bench. That discipline makes room for the family stories and the geological reports to inform one another without pretending they use identical maps.
A comparison with Chino sharpens Tyrone’s character. Both are large porphyry copper systems shaped by intrusive rock and later enrichment, but they occupy different mountain blocks and developed through different companies, towns, and mine plans. The old Azure turquoise area is a particularly Tyrone feature; the vanished Santa Rita town is central to Chino’s story. Those human facts should stay attached to the correct deposit. The chemistry of copper can look broadly similar across a region while the consequences on the ground are local. A shared industry never makes two places historically interchangeable.
Sources and further reading
- New Mexico Bureau of Geology, Tyrone mine tour, for location, geological sequence, mining milestones, and reclamation imagery.
- Elliot Gillerman, Mineral Deposits of Western Grant County, for the older Burro Mountains mineral districts and named workings.
- New Mexico Bureau of Mines, The Metal Resources of New Mexico and Their Economic Features Through 1954, for early Phelps Dodge acquisitions and the 1941 underground-leaching preparation.
- New Mexico Bureau of Geology, “Turquoise in New Mexico”, for the nearby gem deposits and their ownership context in 1979.
- Freeport-McMoRan, North America operations, for current operator descriptions; verify time-sensitive information there.