POST MINING MINERALS FOUND AT BISBEE, ARIZONA
Post-mining calcite was also widely distributed and common in the majority of the mines, typically forming small stalactites and thin flowstonelike ribbons on mine walls. Oddly, post-mining few crystals of calcite, other than microscopic size, are known from Bisbee. Very few post-mining calcite specimens from here were of interest to collectors.
Most stalactites above aragonite “bird’s nest” formations were calcite. Calcite also formed as thin “raft” forms on top of ponded clean water. Calcite was noted coating a long abandoned mine car under a small, but steady flow of water on the Tunnel level of the Higgins Mine, a most unusual occurrence. In Figures 36 and 37 are two photographs of this mine car taken a bit more than 40 years apart.
Figure 34: Post-mining calcite deposited by steadily seeping water along a wide fault zone. 2200 level, Junction Mine.
Figure 33: (right) Typical post-mining calcite as small stalactites and flowstone on slightly altered Martin limestone, 6 level, Southwest Mine, view – 1.4 meters
Figures 36 & 37: (left top) Postmining calcite growth on a mine car, Higgins Mine, Tunnel level in 1967. More than 1/2 inch of calcite had been deposited in the just over 20 years since this mine closed.
(left bottom) The same mine car some 40 + years after the first photo; illustrating the relatively rapid calcite deposition.
The calcium carbonate rich water is flowing from a small diameter diamond drill prospecting hole.
Figure 36: (left) A close-up view of the post-mining calcite in Figure 35, above on the 2200 level, Junction Mine. View – 30cm. Note the oriented growth direction. It was into the strong airflow caused by the mine ventilation, as a huge fan was less than 100 meters distant at the Junction Shaft.
Figure 39: Malachite as a replacement rind on recrystaline Escabrosa Limestone, specimen 13 cm.
Figure 38: Colorless to white, post-mining calcite on post-mining light blue aragonite, 6 level, Southwest Mine. Specimen – 9 cm.
Low pH, copper laden mine waters were a significant problem at Bisbee as early as 1890 when the mining of deeper ores exposed areas undergoing sulfide oxidation. Some of the water contained several tens of pounds of dissolved copper per thousand gallons of water. Any iron or steel tool or mine rail that was in this water for even a short time, was attacked with the iron going into solution and a useless copper form left in its place. Control of acidic mine waters, locally referred to as “copper water,” was a critically important operating issue, even to the end of mining in 1975.
During mining early on, it was a common practice was to channel the acidic, metal-rich solutions through old, abandoned workings, including gobbed (backfilled) stopes, to eventually bring them to a pump station for removal to the surface for copper recovery, via iron precipitation. The gob in
the early stopes was typically a mix of mine waste rock, much of it hand-cobbed limestone, sorted during mining. As early mining took place close to the Sacramento Stock Complex, hydrothermally altered limestone and porphyry waste were common in the gob as well.
It did not take long for the acidic waters to attack the limestone chunks, leaving a replacement veneer of usually malachite, Cu22+(CO3)(OH)2, to several centimeters thick. In some cases, the typical process for forming malachite occurred with the development and transport copper carbonate solutions, typically gel-like, to open spaces for deposition. Such material is usually indistinguishable from most banded malachite. In gob exposed during the mining of the Lavender Pit mine,
Figure 40: Malachite as an impure replacement rind on Martin Limestone. Note the relic features of the limestone are preserved in the replacing malachite. Specimen – 7 cm.
one of the authors found a piece of thick, banded malachite with a rusted track spike imbedded within, reflecting its post-mining origin.
Sufficient copper was deposited in a number of cases to make the gob ore grade (Bateman, et al. 1914). Douglas (1909) did not recognize the process and suggested that what was now ore had been placed as fill in the past. This also caused an erroneous belief among miners that “the old timers used malachite as a backfill,” a local myth that persist to this day.
Several other copper minerals were deposited as well by the “copper water” passing through the gobbed stopes with copper and cuprite fairly common as well as minor azurite. Bateman, et al. (1914) noted that the acidic solutions altered the less reactive rock in the fill to several of the clay minerals such as kaolinite and halloysite.
Figure 41: One of the authors on the 3 level, Southwest Mine where azurite being deposited in a gel-like flow from fractured limestone.
Other carbonate species that have been noted forming with azurite under post-mining conditions include aurichalcite. Post-mining aurichalcite (Zn,Cu)5(CO3)2(OH)6: was observed forming over the period of just a few days along with azurite and malachite. The aurichalcite was formed from a thin jellylike mass running into an open space and drying in a 30-cm wide goethite seam bounded by limestone (Tenney, 1913).
Hydrozincite, Zn5(CO3)(OH)6, has been noted as a localized post-mining flow from the alteration of massive sphalerite in the Copper Queen Mine. It was also reasonably abundant as an alteration product of the massive sphalerite used as waste backfill in a small stope on the “B” level of the Copper Queen Mine. At the time the Copper Queen Mine was operating (1880-1888), the limited zinc mineralization found was not of any economic importance, and thus they were discarded as waste.
Post-mining azurite, Cu32+(CO3)2(OH)2, at Bisbee was rare. No doubt, this was a function of the higher CO2 required for deposition than is typically found in normal mine atmospheres. Nonetheless, in a few instances it has been recognized as a surficial replacement or along fractures in limestone along with more abundant malachite. Subaerial deposits of azurite seem to mimic malachite in that they are quite gel-like when deposited.
In one extraordinary occurrence on the 3rd level of the Southwest Mine, where solutions emerging from a fracture had deposited botryoidal azurite over an area of more than a meter. While it was but a thin crust of three to four millimeters thickness, it was strikingly beautiful.
In other environments, malachite often developed as a thin, often scaly, crust on limestone or calcite when copper-rich solutions flowed over them or in the residual broken rock adjacent to oxidizing sulfides in mined-out stopes. On rare occasion, stalactites of malachite formed on the edge of a broken rock face. In one instance, malachite was apparently being co-deposited with chrysocolla, as modest amounts of copper-laden water were comingled, with one part coming from a silica breccia and the other from fresh limestone. However, in general, post-mining malachite from Bisbee was seldom collected, as it was typically less than inspiring.
Figure 42: One of the authors on the “B” level, Copper Queen Mine where ultraviolet lighting causes the massive sphalerite to fluoresce orange-red, calcite gives a red color while the post-mining hydrozincite responds to UV light with a blue-white fluorescence, and can be seen at center left.
As noted, malachite, azurite and aurichalcite formed from gelatinous materials that typically oozed slowly and in small amounts from cracks as well as other small openings. Chrysocolla (Cu2+,Al)2H2Si2O5(OH)4 .nH2O, formed in a similar manner. Indeed, post-mining chrysocolla was quite common, having been found in several mines as light blue stalactitic growths and as bright blue-green flows on opening walls. Without exception, this material crazes and becomes much paler in color due to desiccation when collected and taken to the surface
Figure 44: (right Chrysocolla and iron hydroxides coating mine timbers at a chute.
7 level, Southwest Mine, vertical view - 1.30 meters.
The exposure of unstable, non-sulfide minerals to the atmosphere during mining also resulted in the formation of post-mining species, often quickly. Nantokite, CuCl, and tolbachite, Cu2+Cl2 both copper chlorides, would react with the humid mine air to form paratacamite, Cu22+(OH)3Cl, in a matter of a few hours. In one case, a seven-centimeter cuprite nodule with a nantokite core developed a soft ram’s horn of scaly paratacamite three centimeters high in less than 20 hours.
Figure 43: (left) Chrysocolla and malachite being deposited simultaneously.
Silica-rich solutions are coming from a silica breccia on the left, while carbonate-rich solutions are flowing from limestone on the right side.
6 Level, Southwest Mine, longest stalactite – 9 cm
Figure 45: Paratacamite as a 8 cm., mushy extrusion from a cuprite nodule, which formed in less than 20 hours upon exposure to the humid mine atmosphere. In situ photo. 14 stope, 5 level, Southwest Mine
As noted above, low pH, copper laden waters were common in the mines at Bisbee. In reality, these waters were solutions resulting from the oxidation of the variable and complex sulfide minerals and contained a variety of dissolved metals but, mostly iron and copper. The pH of these waters was quite variable, depending on the source and, of course, dilution, but pH ranges from below two and less than four were common. If not controlled, “copper water,” (a local term that will be collectively applied herein) was bad stuff, yet it was both a bane and a blessing.
From a safety standpoint, there was nothing more uncomfortable than copper water in the eyes. From personal experience, we can say it was as painful as most any minor injury and temporarily debilitating. Skin burns from strong copper water or prolonged contact with it were unfortunately too common and took time to heal. These were much like burns from sulfuric acid.
Operationally, everything this water contacted was damaged, iron and steel most of all. Thus, care was always taken to control the flow of copper water to keep it away from the mine rail and pipe. The water was then channeled or pumped to recovery plants to extract the copper via iron replacement precipitation. Many millions of pounds of copper were produced at Bisbee in this manner.
However, once mining in an area was completed, the control of such water was no longer a priority and small areas would pond, often covering the now abandoned rail and all else left behind. Copper quickly began to replace the iron and steel. Initially, the original form of the replaced item is often apparent however, copper growth would continue as a direct precipitation of small crystals from concentrated solutions, now expanding the size of the copper mass and eventually obliteration the original form.
Figure 46: Front and back views of mine rail replaced by copper and expanding beyond the replaced steel, 2200 level, Campbell Mine, specimen - 10cm.
Figure 47: Copper which formed as a direct precipitation from solutions and not replacing steel or iron, 2200 level, Campbell Mine, 14 cm.
Figure 48: Gypsum on post-mining copper that precipitated directly from high copper solutions. 2200 level, Junction Mine.
Mass of copper thus formed could easily exceed by ten times the volume of the original iron. Oft times, miners would collect these copper masses and sell them as “native copper”. In general, these pieces were relatively bright in appearance, reflecting their time in an acid environment. The expansive Junction and Campbell mines were the sources of most of these coppers, but all of the sulfide containing mines produced similar material.
Figure 49: Copper deposited on mine timber. Lavender Pit Mine; longest piece – 11 cm
In a few cases, copper would precipitate directly from concentrated solutions without forming around a replaced iron or steel core. Examples are shown above in Figures 42 and 43. These pieces tended to be composed of aggregates of tiny crystals that were more open, even spongelike or in radiating forms and could easily be confused with naturally occurring copper. This potential confusion was often compounded by one to two millimeter cuprite crystals that commonly accompanied these interesting pieces.
Copper directly precipitated on mine timber was found in the Lavender Pit Mine as it encroached upon old underground working of the Sacramento Mine. To preclude the unpleasant task of pumping these acidic waters from the pit, mine planning efforts always kept a low point in the pit over abandoned underground workings, which served as a drain for the mine. All of this water was collected on the 1600 level of the Sacramento Mine and directed to a pump station on the 1800 level Junction Mine for recovery. Over time, copper to five millimeters thick was deposited in voids of the usually badly broken timber. Much of this material was collected by the mine workers as the pit advanced.
Fire developed minerals:
Mine fires were a constant problem in the district once the primary sulfides were exploited to any degree (Mitke, 1920). Pyrite would generate substantial amounts of heat during decomposition to the point of occasionally spontaneously combusting and igniting the supporting timber. The burning sulfides were a real problem because with adequate oxygen, they could burn for a very long time, emitting toxic gases, while denying access to ore in the fire area. Many of these fires defied all efforts to extinguish them and burned for years. Mine fires in both the Briggs and Campbell were contained, but still burning at the time the mines were closed.
Minerals produced as a result of mine fires at Bisbee have not been thoroughly studied. The few species recognized have been noted more by chance than by design. This is because of the lack of access to the areas under conditions that allowed study. Unlike Jerome, Arizona, the fires in the mines at Bisbee were never exposed to the surface by mining. While a number of fire areas were later mined underground, they had been flooded up to the time of reentry or had been filled with a slurry of mill tailings to allow access (Sherman, 1918; Mills, 1958). This destroyed the soluble minerals that might have formed. However, anthonyite from the Dallas Mine may well have been formed as a result of the sulfides that burned in a nearby stope during a mine fire (Anthony, et al. 1995).
The 1948 fire in the Campbell mine, which started on the 2200 level, spread quickly and soon reached the 1300 level. It was eventually vented to the surface through the Oakland shaft, which had been developed for that reason (Mills, 1958) and much of the fire areas reclaimed. Portions of the 1300 level were still very hot, if not burning, in the mid-1970s. The workings closest to the fire, through which the hot gases passed, had their limestone walls somewhat calcined, producing a very impure lime (<30% available CaO on analysis). Post-mining gypsum in a nearby area was converted to anhydrite, and in another area, tiny sulfur crystals were deposited on the mine walls. No other fire related minerals were noted during the single visit by one of the authors in 1975 to the accessible portions of the exhaust workings. Dangerously high levels of carbon monoxide gas and temperatures in excess of 55o C prevented a complete inspection.
The post-mining mineralogy of Bisbee is incomplete, at best. During the operational period of these wonderful mines, few took the time to look at was so common around them and the focus of the miners and collectors was always on the “Bisbee Classics.” Today, some 40 years after the mines closed, most sulfide zones are deep underwater and the rest of the mine workings are far too dangerous to even consider entering. Perhaps the Lavender Pit may produce additional, if not new species, but it too is hazardous.
Yet, in spite of their general unattractiveness and typical instability, some specimens were collected during operations. Perhaps upon further examination these will add to the information base in this neglected area of Bisbee’s mineralogy.
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