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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 in central Colorado. It is spatially related to the mid Oligocene to Miocene composite Climax Stock which was introduced as multiple pulses over the period from 33 and 18 Ma. The mineralised stock cuts 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).
The Climax Stock is centred on the intersection of a NNE trending anticline and a north-south syncline, both of Proterozoic age. The stock also lies immediately adjacent to the major NNE trending, west dipping, normal, Mosquito Fault which has displaced parts of the orebody by 2700 to 3000 m. The Climax Stock has plan dimensions of 1100 x 800 m and was apparently introduced in five main phases, comprising:
The South-west Mass, an elliptical body of the order of 550x350 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 Central Mass, which is present 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. Phases of this mass have been dated at 29.8±0.4 Ma;
The Lower Intrusive Series - this series occurs as two nested, stock-like bodies that form a cupola beneath the Lower Orebody, and concentrically within and below the Central Mass. 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, 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;
The Seriate Granite, 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. This granite is dated at 18.2±0.9 Ma (White, et al., 1981).
Mineralisation & 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 South-west Mass, the Upper Orebody to the Central Mass of the Climax Stock, and the Lower Orebody to the deeper phase of the Stock, namely the aplite porphyry of the Lower Intrusive series. 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% MoS2, (Wallace and Snow, 1989).
Reserve 1987 - 310 Mt @ 0.30 to 0.35% MoS2, (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.
For detail consult the reference(s) listed below.
The most recent source geological information used to prepare this summary was dated: 1995.
Record last updated: 26/8/2013
This description is a summary from published sources, the chief of which are listed below.
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