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35-459: The Harding Pegmatite Mine is a former adit mine that extracted lithium , tantalum , and beryllium from a Precambrian pegmatite sill . It ceased operations in 1958 and its owner, Arthur Montgomery, donated it to the University of New Mexico , which runs the site as an outdoor geology laboratory with mineral collecting permitted on a small scale. Although the quartz pegmatite had attracted

70-516: A belt about 2500 feet long and 150 to 500 feet wide. Radiometric ages are somewhat discordant, ranging from 1260 Mya for four Harding muscovites to 1350 Mya for a Harding lepidolite. A more recent "average age" is given as 1336 Mya, and discrepancies may be due to contamination from the host rock. However, the pegmatite is thought to be up to 100 million years younger than any nearby granite plutons and does not seem to be genetically associated with any of them. The main mine workings are exposed over

105-506: A certain amount of contact metamorphism by adjacent granitic masses. Metamorphosed basalt ( metabasalt ) creates ortho-amphibolite and other chemically appropriate lithologies create para-amphibolite . Although tremolite is a metamorphic amphibole, it is most commonly derived from highly metamorphosed ultramafic rocks , and thus tremolite-talc schist is not generally considered a variety of amphibolite. A holocrystalline plutonic igneous rock composed primarily of hornblende amphibole

140-479: A crew of four men to mine and hand sort the ore, which was taken out on "Beryl", the mine's mule. Production totaled 690 tons of high-grade ore with 11.2% beryllium oxide and 184 tons of lower-grade ore with 5.5% beryllium oxide, as well as small production of lepidolite. The Harding pegmatite intrudes along the boundary between the amphibolite and schist facies of the Vadito Group . The various outcroppings form

175-549: A length of about 1100 feet and a breadth of up to 250 feet. The pegmatite is zoned subhorizontally into the following zones: These zones are mirrored at the base of the pegmatite, except that the lower zones tend to be poorer in beryl and more aplitic than pegmatitic. The abundant fine-grained albite is sugary in appearance. Additional accessory minerals, of no economic importance but of interest to mineral collectors, include almandine , spessartine , and pyrochlore . Geochemical analysis and analysis of fluid inclusions suggests

210-436: A metamorphic amphibolite, it must be certain that the amphibole in the rock is a prograde metamorphic product, and not a retrograde metamorphic product. For instance, actinolite amphibole is a common product of retrograde metamorphism of metabasalt at (upper) greenschist facies conditions. Often, this will take on the crystal form and habit of the original protolith assemblage; actinolite pseudomorphically replacing pyroxene

245-458: A mine : in simple terms, cool air will enter through an adit, be warmed by the higher temperature underground and will naturally exhaust from vertical shafts, some of which are sunk specifically for this purpose. Most adits are designed to slope slightly upwards from the entrance so that water will flow freely out of the mine. Mines that have adits can be at least partly drained of water by gravity alone or power-assisted gravity. The depth to which

280-514: A mine can be drained by gravity alone is defined by the deepest open adit which is known as the "drainage adit". The term mine drainage tunnel is also common, at least in the United States. Workings above this level (known as "above adit") will remain unflooded as long as the adit does not become blocked. All mine workings below both the drainage adit ("below adit") and the water table will flood unless mechanical means are used for drainage. Until

315-460: A response to late-stage pressure release. Saline brines caused lepidolite replacement at temperatures near 265 °C. Finally, small pockets of quartz, feldspar and microlite were crystallized. In 1974, Arthur Montgomery offered to donate the property to the University of New Mexico. The university leased the property for four years while making numerous improvements, which include a walking tour of

350-404: A ton per day, in spite of the difficulties of hand sorting the beryl from the nearly indistinguishable feldspar and quartz gangue . In 1950 and 1951, beryl production exceeded 150 tons, making New Mexico the leading beryl-producing state. Production averaged 100 tons per year until 1950, when the death of Montgomery's partner, Flaudio Griego, ended mining operations. Operations were simple, using

385-630: Is about ten miles (16 km) long. Other examples are the Great County Adit in Cornwall, a 40-mile (64 km)-long network of adits that used to drain the whole Gwennap mining area, and the 3.9 miles (6.3 km) Sutro Tunnel at the Comstock Lode in Virginia City , Nevada . A side benefit of driving such extensive adits is that previously unknown ore-bodies can be discovered, helping finance

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420-423: Is almost always granted) and release forms. Adit Adits are driven into the side of a hill or mountain, and are often used when an ore body is located inside the mountain but above the adjacent valley floor or coastal plain. In cases where the mineral vein outcrops at the surface, the adit may follow the lode or vein until it is worked out, in which case the adit is rarely straight. The use of adits for

455-507: Is an indication that the amphibolite may not represent a peak metamorphic grade in the amphibolite facies. Actinolite schist is often the result of hydrothermal alteration or metasomatism , and thus may not, necessarily, be a good indicator of metamorphic conditions when taken in isolation. Second, the microstructure and crystal size of the rock must be appropriate. Amphibolite facies conditions are experienced at temperatures in excess of 500 °C and pressures less than 1.2 GPa, well within

490-496: Is called a hornblendite , which is usually a crystal cumulate rock . Igneous rocks with greater than 90% amphiboles, which have a feldspar groundmass , may be lamprophyres . Metamorphic rocks composed primarily of amphibole , plagioclase , with subordinate epidote , zoisite , chlorite , quartz , titanite , and accessory leucoxene , ilmenite and magnetite which have a protolith of an igneous rock are known as ortho-amphibolite . Para-amphibolite will generally have

525-469: Is distinctive, the pyroxene altered to fuzzy, radially arranged actinolite pseudomorphically after pyroxene, and saussuritised plagioclase. The archaic term epidiorite is sometimes used, especially in Europe, to refer to a metamorphosed ortho-amphibolite with a protolith of diorite , gabbro or other mafic intrusive rock. In epidiorite the original clinopyroxene (most often augite ) has been replaced by

560-504: Is often preserved. Amphibolite facies equilibrium mineral assemblages of various protolith rock types consist of: Amphibolite facies is usually a product of Barrovian Facies Sequence or advanced Abukuma Facies Sequence metamorphic trajectories. Amphibolite facies is a result of continuing burial and thermal heating after greenschist facies is exceeded. Further burial and metamorphic compression (but little extra heat) will lead to eclogite facies metamorphism; with more advanced heating

595-588: Is recommended by the British Geological Survey when it is possible to determine the origin of the rock from its characteristics alone (and not from field relationships), particularly when the degree of metamorphism is low. Amphibolite as a rock defines a particular set of temperature and pressure conditions known as the amphibolite facies . However, caution must be applied here before embarking on metamorphic mapping based on amphibolite alone. First, for an ortho-amphibolite or amphibolite to be classed as

630-415: Is required to transport miners and heavy equipment into and out of the mine. It is also much easier to bring ore or coal out of the mine. Horizontal travel by means of narrow gauge tramway or cable car is also much safer and can move more people and ore than vertical elevators. In the past horses and pit ponies were used. In combination with shafts, adits form an important element in the ventilation of

665-640: Is typically dark-colored and dense, with a weakly foliated or schistose (flaky) structure. The small flakes of black and white in the rock often give it a salt-and-pepper appearance. Amphibolite frequently forms by metamorphism of mafic igneous rocks, such as basalt . However, because metamorphism creates minerals entirely based upon the chemistry of the protolith , certain 'dirty marls ' and volcanic sediments may also metamorphose to an amphibolite assemblage. Deposits containing dolomite and siderite also readily yield amphibolite ( tremolite -schist, grunerite -schist, and others) especially where there has been

700-588: The Embudo Mining Company was organized by J.L. Danziger and began construction of a mill near Embudo. This was completed and mining resumed in 1927. The main ore body was mined out in 1929 and the mine closed again in 1930. About 3,500 tons of ore were produced with a value of about $ 140,000. This represented a modest profit over the three years of mill operations but a net loss for the entire period of mining. High demand for tantalum in 1942 for wartime production, and reports going back to 1931 of microlite at

735-458: The Harding Mine, led Arthur Montgomery to investigate the old workings. He found considerable rich material in the mine dumps and at the east end of the workings, and he obtained a lease purchase contract on the mine property. With a team of six local miners, ore was extracted with chisels and sorted by hand. Concentration of the small but rich quantity of highly valuable ore was problematic, but

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770-468: The U.S. Bureau of Mines Testing Laboratory in Rolla, Missouri, used an experimental gravity separation method to process 33.5 tons of ore and extracted 6137 pounds of 77.55% niobium-tantalum oxide. This was the largest unit of U.S. tantalum production ever recorded. However, a small mill built at Rinconada failed to meet its rated capacity of 12 tons per day. Lithium ores were also mined during this period, and by

805-460: The U.S. Bureau of Mines drilled 39 exploratory cores south of the main workings. The cores showed enough content of spodumene and tantalum-niobium minerals to be classified as milling-grade ore. This made the Harding the first U.S. pegmatite mine to have blocked-out reserves. These are still in place and could conceivably be mined in the future. Beryl had been recognized as a minor accessory mineral at

840-434: The amphibolite appears to transgress apparent protolith bedding surfaces it is an ortho-amphibolite, as this suggests it was a dyke . Picking a sill and thin metamorphosed lava flows may be more troublesome. Thereafter, whole rock geochemistry will suitably identify ortho- from para-amphibolite. The word metabasalt was thus coined, largely to avoid the confusion between ortho-amphibolite and para-amphibolite. This term

875-528: The attention of prospectors since before 1900, the extensive deposits of lepidolite were not recognized until 1918 by Joseph J. Peyer. Peyer and his partners mined the ore body with explosives, sorted the ore by hand, and hauled the ore to Embudo by wagon, where the nearest rail line was located. At that time, the chief use of lithium was in specialty glass . However, the ore was contaminated with unrecognized tantalite which caused serious difficulties with its use, and production ceased in 1924. That same year,

910-522: The ductile deformation field. Gneissic texture may occur nearby, if not then mylonite zones, foliations and ductile behaviour, including stretching lineations may occur. While it is not impossible to have remnant protolith mineralogy, this is rare. More common is to find phenocrysts of pyroxene, olivine , plagioclase and even magmatic amphibole such as pargasite rhombohedra, pseudomorphed by hornblende amphibole. Original magmatic textures, especially crude magmatic layering in layered intrusions ,

945-472: The enormous cost. Adits were used in Cornwall before 1500, and were important to the tin and copper mines in Cornwall and Devon because the ore-bearing veins are nearly vertical, thus acting as ingress channels for water. Amphibolite Amphibolite ( / æ m ˈ f ɪ b ə l aɪ t / ) is a metamorphic rock that contains amphibole , especially hornblende and actinolite , as well as plagioclase feldspar , but with little or no quartz . It

980-450: The extraction of ore is generally called drift mining . Adits can only be driven into a mine where the local topography permits. There will be no opportunity to drive an adit to a mine situated on a large flat plain, for instance. Also if the ground is weak, the cost of shoring up a long adit may outweigh its possible advantages. Access to a mine by adit has many advantages over the vertical access shafts used in shaft mining . Less energy

1015-505: The invention of the steam engine this was the main restriction on deep mining. Adits are useful for deeper mines. Water only needs to be raised to the drainage adit rather than to the surface. Because of the great reduction in ongoing costs that a drainage adit can provide, they have sometimes been driven for great distances for this purpose. One example is the Milwr tunnel in North Wales, which

1050-439: The majority of rocks begin melting in excess of 650 to 700 °C in the presence of water. In dry rocks, however, additional heat (and burial) may result in granulite facies conditions. Uralite is a particular hydrothermally altered pyroxenite ; during autogenic hydrothermal circulation the primary mineralogy of pyroxene and plagioclase , etc. has altered to actinolite and saussurite ( albite + epidote ). The texture

1085-537: The mine from its inception. However, this was so easily confused with the abundant albite and quartz of the pegmatite that it was not until 1942 that the U.S. Geological Survey recognized that beryl was abundant at the mine. In 1944 Montgomery found a single block of beryl weighing almost 100 pounds at one of the dumps, then uncovered a lens of beryl at the west end of the workings. This produced 23 tons of ore containing 11% beryllium oxide. However, full-scale beryllium mining did not begin until 1950. Ore production reached

Harding Pegmatite Mine - Misplaced Pages Continue

1120-426: The mine. Because the mine property included both patented and unpatented claims, transfer of the title required an act of Congress (Senate Bill 1403). The United States retains the right to mine strategic minerals should it become necessary for the security of the United States. Persons wishing to visit the mine must contact the chairman, Department of Geology, University of New Mexico, 87131 to obtain permission (which

1155-417: The pegmatite was injected at temperatures near 600 °C at a depth of 6.0 to 7.5 km (2.0 to 2.5 kbar). The primary zones crystallized under closed-system conditions a temperature of 525 to 425 °C. A separate immiscible CO 2 -H 2 O volatile-rich fluid was present in the pegmatite system during crystallization of the primary pegmatite zones. The sugary albite zone formed from a residual Na-rich magma as

1190-453: The same equilibrium mineral assemblage as ortho-amphibolite, with more biotite, and may include more quartz, plagioclase, and depending on the protolith, more calcite / aragonite and wollastonite . Often the easiest way to determine the true nature of an amphibolite is to inspect its field relationships; especially whether it is interfingered with other metasedimentary rocks, especially greywacke and other poorly sorted sedimentary rocks. If

1225-428: The time mining paused in 1947, the mine had yielded 41 tons of high-grade spodumene , 558 tons of lepidolite ore, nearly 500 pounds of placer tantalite-columbite containing an average of 43% tantalum oxide, and 22,116 pounds of microlite concentrates containing an average of 68% tantalum oxide and 7% niobium oxide. The operations were profitable enough to allow Montgomery to purchase the property outright. During 1943,

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