By Robert Gay
The historic Lead Queen Mine in the Patagonia Mountains, which produced lead, silver and small amounts of copper between 1898 and 1940, has intermittently leaked toxic minerals, both visible and invisible, ever since.
In 2014, monsoon rains caused a dramatic orange outflow that attracted media attention, followed by two Coronado National Forest (CNF) projects attempting to detoxify the flows.
What’s the status of the mine in 2020? In 2019 CNF installed a “hydraulic plug” at the tunnel entrance, or adit, in all probability closing outflow for good and stopping a major source of acidic drainage into a tributary of Harshaw Creek. A mid-January 2020 visit confirmed that there appears to be no new seepage coming directly from the former adit opening.
The Forest Service project at the Lead Queen also included significant surface remediation. Earthmoving to the tunnel covered the plugged mouth with a slope shaped like a natural grade. The approach route, starting at a newly improved turnaround, was also graded in a natural-appearing way, eliminating the formerly drivable access to the mine opening.
On the steepest of the entry slopes there were straw wattles to help with erosion prevention. Across the stream a relocated pile of tailings, estimated at 30 tons, was shaped like natural ground and given a soil cover.
The regraded surfaces, about a half-acre in all, were left rough and a little scarified with some random placement of small and medium rocks. All but the rocky bottom of the streambed was seeded with a straw and fiber mix that the CNF “Fact Sheet” on the project (July 2019) described as including local wildlife seeds. Few plants have sprouted over the fall and winter, but during spring and monsoon season new plants are expected to appear. No plants were transplanted in for this project.
Monitoring over decades will be needed before the project revegetation can be called fully successful. The surface-healing and revegetation part of this project could potentially become an example of creative and scientifically informed restoration processes which enhance wildlife habitat and return disturbed ground to nature.
There was evidence at the January visit of a low flow of clear water coming from upstream of the mine near the former mine entrance. Below the former adit a small yellow-orange flow was observed that continues downstream. Within about 200 feet, the stream water became white with tinges of green; further downstream along Forest Service Road 4684, white coloring is visible in the stream bed as far as Harshaw Rd.
Dave Ellis, of Patagonia, who volunteers for the Patagonia Area Watershed Study, explained the white precipitate was non-toxic. “The white sludge” Ellis said, “is calcium carbonate precipitate.” This reaction can occur when very acidic water meets more neutral stream water, or even when rainwater meets acidic water.
Chemically, the reaction is a move toward neutralization, so the incoming acidic water ends up less acidic. Additionally, some of the reactions liberate CO, a gas which likely explains the white foam occasionally spotted in the numerous other local washes.
Calcium carbonate occurs naturally in limestone, marble, chalk and seashells and is not considered a problem for living creatures. However, the stream bed below the mine has been accumulating many dissolved minerals, mostly invisible, in its 80 years of seasonally varying flows since the Lead Queen stopped production in 1940. These include, as local environmentalist Gooch Goodwin explained, “quite a mineral soup of heavy metals.”
Among minerals in mine drainage that were studied in a University of Arizona Master’s thesis project by Susan Ann Dean in the Patagonia Mountains are sulfates (a sulfur-based salt), iron, copper, manganese, zinc, arsenic, lead, cadmium, chromium, selenium, mercury, silver, aluminum.
The study concluded that just as the minerals in the ground around here are wildly varied, so also are their levels in water in different places, sometimes being negligible and other times being above acceptable levels for humans.
Mineral levels change with the season, the distance from a mine, the amount of flowing water they are in, the rock they flow over, and the acidity of water they are found in. Except for a little seepage into the ground, all are being moved downstream, dropping out here and there as they head to the large settling basin of Patagonia Lake, which has been chemically researched in the past by United States Geological Survey (USGS) geo-hydrologist Floyd Gray and others.
Questions have been raised about the long-term public health effects of these water-borne minerals to local residents, but extensive epidemiological studies have yet to be conducted. The long-term biological effects of multiple minerals dispersed into local watersheds are not fully understood, whether for humans, for cattle, horses or any other species. A strong case exists for further research into the complex hydrology and biochemistry of the entire watershed.