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The Climax porphyry molybdenum mine is located 105 km WSW of Denver and 20 km NE of Leadville in central Colorado, USA (#Location: 39° 22' 11"N, 106° 10' 15"W).

The original claim at Climax was pegged for gold in 1890, although molybdenum was not recognised until 1895. Molybdenum mining commenced in 1916, but ceased in 1918 due to a lack of demand. The operation started again in 1924 and progressively increased capacity through the century. It is one of the highest grade large scale bulk mining Mo deposits in the world and has been operated both as an open pit and more recently as a block cave underground mine. In 1978 open pit production was 7 Mt of ore per annum, with a waste:ore ratio of 1.6:1, while an additional 9.8 Mt was extracted from underground.   The mine was closed during the 1980's.


The Climax molybdenum orebody lies within the Colorado Mineral Belt of central Colorado. This belt hosts some of the largest and economically most important molybdenum deposits in the world, including Urad-Henderson and Mount Emmons. The emplacement of Climax-type granites (White et al., 1981) and the formation of porphyry molybdenum deposits is the product of incipient extension related to the development of the Rio Grande Rift System (e.g., Wallace et al., 1968; Wallace 1995; Lüders et al., 2009). These porphyry molybdenum deposits appear to have formed from leucogranitic magmatic fluids that were high in fluorine and produced large-scale silicification and precipitation of quartz veins above the magmatic stocks (e.g., White et al., 1981; Bookstrom et al., 1988).

The rocks in the Colorado Mineral Belt are divided by the NNE trending, 75 to 80°W dipping Neogene Mosquito normal fault, with Proterozoic basement to the east and Paleozoic sedimentary rocks to the west. The latter are down faulted by ∼2700 m (McCalpin et al., 2012 ) relative to the basement and consist of conglomerate, sandstone and shale with interlayered limestone beds. The basement comprises late Palaeoproterozoic (1800 to 1700 Ma) metamorphics of the Idaho Springs Formation, and the Mesoproterozoic (1350 to 1480 Ma) Silver Plume Granite. The Idaho Springs Formation comprises biotite schist and gneiss, and banded granite gneiss and granulites, while the Silver Plume Granite is made up of three separate but closely related phases, occurring as stocks, dykes and sheets of medium grained granite and pegmatite, and fine to medium grained equigranular granite. Regionally these are overlain by the Phanerozoic of the Interior Platform and Mesozoic to Cainozoic Foreland Basins. These latter sequences are believed to have been present during the emplacement of the Climax Stock, but subsequently removed by post-ore uplift and erosion (Wallace, et al., 1968; Wallace, et al., 1989).

Between 45 and 35 Ma, quartz monzonitic and monzodioritic dykes, stocks and sills were emplaced both in the Proterozoic basement and in the Palaeozoic sedimentary rocks. These intrusions are related to the waning stages of the Laramide Orogeny and are locally mineralised with Ag, Pb and Zn, plus minor Cu and Au (Bookstrom, 1989). In the subsequent atectonic regime, between the end of Laramide compression and the beginning of rifting along the Rio Grande Rift, silica-rich magmas were emplaced between 35 and 25 Ma along with minor mafic alkaline magmas ( Bookstrom, 1981, 1989; Bookstrom et al., 1988). This intrusive sequence commenced at 34.9±4.0 Ma with very leucocratic, crystal-poor rhyolite dykes in the eastern part of the area, referred to as the ‘late white rhyolites of the Alma district’ by Bookstrom et al. (1988 )

Mineralisation at Climax is spatially related to the subsequent mid Oligocene to Miocene composite Climax Stock which was introduced as multiple pulses over the period from 33 and 18 Ma. The stock is centred on the intersection of a NNE trending anticline and a north-south syncline, both of Proterozoic age. It also lies immediately adjacent to the Mosquito Fault and has plan dimensions of 1100 x 800 m, apparently introduced at least five main phases granitic porphyry stocks and dykes, comprising:

• The 33.2±2.1 Ma Alicante Stock (or South-west Mass), an elliptical body of the order of 550 x 350 m which is separated from the main stock by up to 120 m in the upper levels, but joins it lower in the mine. It is a biotite poor, fine grained granite to aplite porphyry dated at 33.2±2.1 Ma and made up of around 65% of 0.5 to 7 mm subhedral phenocrysts of quartz, alkali-feldspar and plagioclase in a fine grained (0.01 to 0.15 mm) quartz and alkali-feldspar matrix. Where less altered a possible flow banding is observed. The Alicante stock produced the uppermost Mo ore shell (the 'Ceresco Ore Body'), most of which was removed by erosion;
• The 29.8±0.4 Ma Bartlett Stock or Central Mass, which cuts the Alicante Stock at a depth of ∼200 m and formed the economically important 'Upper Ore Body'. It occurs as a circular mass, increasing in diameter with depth, from around 360 m diameter in the upper levels to 640 m some 180 m lower. It is a coarse grained, biotite poor, commonly foliated (or flow banded) granite porphyry with 40 to 50% of 2 to 15 mm phenocrysts of alkali-feldspar, plagioclase and quartz in a fine (0.05 to 2 mm) granular matrix of quartz, alkali-feldspar, plagioclase, muscovite, biotite and fluorite;
• The 26.1±1.2 Ma Wallace Stock or Lower Intrusive Series that formed the 'Lower Ore Body' - this series occurs as two nested, stock-like bodies that form a cupola beneath the Lower Orebody, and concentrically within and below the Bartlett Stock. Strong silicification associated with the Lower Orebody has destroyed the textures and obscured the contact with the Central Mass. The most extensive phase, the outer biotite granite porphyry intrudes the Central Mass. It is made up of biotite bearing, fine grained granite to aplite porphyry, with 20 to 30% of 0.3 to 4 mm phenocrysts of alkali-feldspar, plagioclase and quartz, set in a 0.01 to 0.15 mm matrix of quartz and alkali-feldspar ±plagioclase, with minor biotite, fluorite and topaz. A second coarser mass with lesser phenocrysts, a biotite porphyry, forms a concentric shell within the biotite granite porphyry. A series of intra-mineral dykes radiating upwards through the cap of the stock and may be related to this phase;
Post-ore Intrusive, also known as the 'Climax late dykes' or 'late leucorhyolite porphyry dykes', which comprise two WNW trending dykes of late rhyolite porphyry in the upper levels of the mine. These coalesce lower in the system to form a single dyke which thickens and may form a central stock at depth, a hundred metres or so across. They are dated at 25.5±1.2 Ma (Bookstrom et al., 1988);
• The 24.4±5.0 Ma Traver Stock, previously known as the Seriate Granite’, Sodic Granite or Porphyritic Granite Phase. It was emplaced at another ∼200 m greater depth than the Wallace Stock, and is a nearly equigranular un-mineralised granite which forms the core of the main stock, although the top sections are obscured by a quartz-topaz-pyrite alteration zone.

Mineralisation and Alteration

Molybdenite at Climax occurs in three distinct, but overlapping stockwork orebodies, each related spatially and temporally to one or more of the four productive phases of the Climax composite stock. These are the Ceresco Orebody, which is the uppermost and oldest, the Upper Orebody, which is below the Ceresco, and the Lower Orebody which is the deepest and youngest. Each is shaped like an inverted bowl or shell, and is circular or annular shaped in plan, and arcuate in section. As outlined by the 0.2% MoS2 grade contour, the ore shells are 150 to 200 m thick with maximum outer diameters in plan of from 900 to 1200 m, each centred on its related intrusive phase of the stock.

The Ceresco Orebody is related to the Alicante Stock, the Upper Orebody to the Bartlett Stock of the Climax Composite Stock, and the Lower Orebody to the deeper phase of the Stock, namely the Wallace Stock. The Upper Orebody is also a composite body, being related to two separate, but close phases of the Central Mass. Low grade tungsten mineralisation occurs in the upper sections of each orebody, and in their hangingwalls, separating them from the overlying Mo orebody. The W bearing veinlets are younger than the accompanying Mo bearing veins of the same orebody (Wallace, et al., 1989).

A separate event, some 1.7 Ma younger than the Lower Orebody, is related to the last porphyritic granite phase (the Seriate Granite). Near its upper margins the granite carries sparse disseminated flakes of molybdenite, above which there is a weakly developed stockwork of sub-ore quartz-molybdenite veins in the hangingwall of the intrusive. Base metals and rhodochrosite are also abundant in this zone (Wallace, et al., 1989).

Molybdenum mineralisation is present in the following forms, i). in quartz filled fractures, generally less than 0.65 cm thick, accounting for 95% of the molybdenum in the Upper Orebody; ii). in tabular quartz veins; iii). disseminated in pegmatite pods and aplite dykes; iv). as irregular clots and sparse scattered crystals in high silica rocks; and v). as 'paint' on thin fractures. The principal ore bearing veinlets are developed in a number of directions in a passive breccia, with a vein density in any one direction of 1 to 3 veins per cm to 1 per 10 cm. There may be up to 4 or more directions of veining in areas of intense mineralisation. Pyrite averages 2 to 3% of the ore and is the most abundant sulphide (Wallace, et al., 1968).

The Climax Stock occupies the core of a local dome, whose formation is interpreted as being related to the intrusion of the stock. This intrusion and dome formation is further interpreted as having been responsible for the passive breccia formed in the cap of the stock, within which the orebodies are emplaced (Wallace, et al., 1968).

Hydrothermal alteration at Climax has been intense in many parts of the mine, particularly the upper 200 to 300 m. Where alteration zones related to Upper Orebody are overprinted by those of the Lower Orebody, textural-destructive alteration of both intrusive and intruded rocks is common. A generalised zonal arrangement of alteration products from the top of the associated intrusive phase, upwards and outwards are:
Footwall silica zone - formed at the apices of the associated intrusion phase, with the rocks above the cupola being replaced by fine grained hydrothermal quartz. Silica flooding is virtually complete over large areas of the footwall of the Upper and Lower Orebodies;
K-feldspathised zone - the orebodies are best developed in the K feldspathised zones above and peripheral to the footwall silicified zones. Conversion of Proterozoic rocks to pinkish-tan feldspar is essentially complete over distances of a few hundred metres in some areas of the mine;
Phyllic zone - outward from the feldspathised zone is a halo of fine grained quartz-sericite rock containing disseminated pyrite. These replacement products are apparently related to quartz-pyrite (sericite) veinlets. A single 0.5 cm veinlet can produce a distinct 8 cm halo on either side of the fracture, in which the rock texture is obliterated. W and Sn are best developed in this zone as is topaz, with common fluorite;
Argillic zone - characterised by kaolinite, montmorillonite and sericite development. The outer margin has a radius of around 750 m;
Propylitic zone - taking the form of weak carbonate, developments, and patchy sericitisation, passing inwards into chlorite and sericite. The outer boundary of this zone forms a halo to the whole system, with the gradation to fresh rock being 2 km to the east and 4 km to the west of Climax, although these zones are cut off to the west by the Mosquito Fault (Wallace, et al., 1989).

The ore is believed to have been emplaced at a temperature of between 500 and 600°C (White, et al., 1981).

Published reserve and production figures at Climax include:

Production, 1918-87 - 421 Mt @ 0.41% MoS
2, (Wallace and Snow, 1989).
Reserve 1987 - 310 Mt @ 0.30 to 0.35% MoS
2, (Wallace and Snow, 1989).
Proven + probable Reserve, 1994 - 132 Mt @ 0.23% Mo (AME, 1995).

Remaining recoverable reserves at December 31, 2011 (Freeport-McMoRan, 2012):
    Proved reserves - 75 Mt @ 0.189% Mo;
    Probable reserves - 112 Mt @ 0.137% Mo;
    Proved + probable reserves - 187 Mt @ 0.158% Mo.

Remaining recoverable reserves at December 31, 2018 (Freeport-McMoRan, 2018):
    Proved + probable reserves - 168 Mt @ 0.15% Mo.

For detail consult the reference(s) listed below.

The most recent source geological information used to prepare this decription was dated: 2015.     Record last updated: 2/4/2020
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.


  References & Additional Information
   Selected References:
Audetat, A.,  2015 - Compositional Evolution and Formation Conditions of Magmas and Fluids Related to Porphyry Mo Mineralization at Climax, Colorado: in    J. of Petrology   v.56, pp. 1519-1546.
Luders, V., Romer, R.L., Gilg, H.A., Bodnar, R.J., Pettke, T. and Misantoni, D.,  2009 - A geochemical study of the Sweet Home Mine, Colorado Mineral Belt, USA: hydrothermal fluid evolution above a hypothesized granite cupola: in    Mineralium Deposita   v.44, pp. 415-434.
Wallace S R, Snow G C,   1989 - The porphyry molybdenite deposits at Climax, Colorado: in Bryant, B. and Beaty, W., (Eds.), 1989 Mineral Deposits and Geology of Central Colorado, Mineral Deposits of North America, 28th International Geological Congress, American Geophysical Union, Washington,   Field Trip Guidebook T129, pp. T129:38-44.
Wallace, S.R., Muncaster, N.K., Jonson, D.C., Mackenzie, W.B., Bookstrom, A.A. and Surface, V.E.,   1968 - Multiple intrusion and mineralisation at Climax, Colorado,: in Ridge, J. (Ed.), 1968 Ore Deposits of the United States, 1933-1967, American Institute of Mining Metallurgy and Petroleum Engineers, New York,   The Graton-Sales Volume, pp. 605-640.

Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge.   It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published.   While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants:   i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and   ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.

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