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Rampura Agucha |
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Rajasthan, India |
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Zn Pb Ag
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Super Porphyry Cu and Au
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The Rampura-Agucha zinc-lead-silver deposit is located in the Bhilwara district of central Rajasthan State in north-western India. It is ~220 km to the SW of the state capital, Jaipur, 240 km to the NE of Udaipur and ~350 km to the SW of Delhi (#Location: 25° 50'N, 74° 44'E).
Published reserve, resource and production figures are as follows:
63.65 Mt @ 13.38% Zn, 1.9% Pb, 45 g/t Ag, 9.5% Fe (Pre-mine, Total Res., 1991, Mine visit, 1996)
52.95 Mt @ 13.53% Zn, 1.96% Pb, 9.52% Fe (Pre-mining Demonstrated Resource, 1991, HZL, 1996)
42.53 Mt @ 13.27% Zn, 1.94% Pb (Pre-mine Resource, to 200 m below surface, HZL, 1996)
3.12 Mt (Transition ore, ie. mixed sulphide & oxide, incl. in reserve, Gandhi, et al., 1984)
2.6 Mt (Gossan, Gandhi, et al., 1984)
45 Mt @ 13.6% Zn, 1.9% Pb (Geological Resource, Nat. Res. Canada website, 2006)
Geology
The Rampura-Agucha deposit falls within the Aravalli Craton of northern Peninsular India. It lies within the broad sheared transition between the Mangalwar and Sandmata Complexes of the Bhilwara Supergroup, some 3 to 4 km from the regional NE-SW trending Delwara Lineament that lies along the contact. The rocks in this zone have been subjected to polyphase deformation and high grade metamorphism (HZL, 1996), with frequent zones of mylonite (Upadyaya, pers. comm., 1996).
The deposit is hosted by the Precambrian Banded Gneissic Complex composed of heterogeneous metamorphics, migmatites, granitoids, pegmatites and mafic rocks of variable composition. All have been subjected to polyphase deformation and metamorphism. This sequence is quoted in different sources as being Lower Proterozoic (2400 to 1700 Ma) or Archaean (3200 to 2500 Ma).
In the deposit area the host rocks strike roughly north-east and dip at 60 to 80° to the south-east. The host sequence from footwall to hangingwall is as follows:
i). mylonite, which is 15 to 40 m thick, paralleling the strike of the sequence and the ore;
ii). granite gneiss;
iii). footwall garnet-biotite-sillimanite gneiss with interlayers of granite-gneiss, foliated amphibolite, hard compacted granulitic calc-silicates and pegmatites;
iv). graphite-mica-sillimanite gneiss/schist, the host to ore; and
v). garnet-biotite-sillimanite gneiss/schist, inter-banded with foliated amphibolites, granulitic calc-silicate and pegmatites.
The gneisses in the sequence exhibit augen structures and relict banding of amphibolites and calc-silicates, ie. of melanocratic and leucocratic material. The garnets are almandine.
The principal lithologies encountered within and adjacent to the Rampura-Agucha ore deposit are as follows:
Garnet-biotite-sillimanite gneiss - this is the most common rock type of the Bhilwara Supergroup within the vicinity of the orebody. It is very heterogeneous and has a streaky, banded augen structure with relict layers of quartzo-feldspathic material, as well as layers of amphibolite and calc-silicates. The principal components are quartz, sillimanite, feldspar and garnet, with K-feldspar dominating over plagioclase. They are in general well foliated and composed of leucocratic bands of quartz and feldspar alternating with melanocratic layers rich in biotite, sillimanite and garnet. Quartzo-feldspathic augen are surrounded by mafic streaks, rich in black mica which define the schistosity. The feldspars are essentially microcline with minor micro-perthite and oligoclase.
Garnets are brownish-red to flesh-red almandine [Fe3Al2(SiO4)3], and highly shattered, sometimes with inclusions of quartz. Garnet and feldspar porphyroblasts are from 'a few' to 100 mm across set in a gneissic to schistose ground-mass (Gandhi,et al., 1984; Ranawat & Sharma, 1990; Sharma & Singh, 1990).
Sillimanite needles form clusters, fibrolites and small bundles on foliation planes encircling the brittle minerals such as quartz, feldspar and garnet, but are also associated with the biotite. Occasionally blades of kyanite may be observed. Biotite, which occurs as tabular aggregates, is the principal mica, with only traces of sericite. Accessories include zircon, apatite, tourmaline and iron oxides (Gandhi,et al., 1984).
Graphite-mica-garnet-sillimanite schist - This rock type is the main host to the mineralisation of the orebody. It apparently has a sharp, shear controlled contacts with both the hangingwall and footwall gneisses and is basically laterally co-extensive with the ore. It is thickest in the central sections of the orebody, apparently pinching out with the ore to the north-east and south-west. It is essentially composed of quartz, micas (mainly biotite with lesser sericite and chlorite), and sillimanite, with an appreciable amount of graphite, as well as minor K-feldspar and garnet. Accessory minerals are apatite and tourmaline. Overall it is green in colour, due to the concentration of chlorite (Gandhi,et al., 1984; Sharma & Singh, 1990). Sillimanite is present within the schist, averaging 3 to 4%, and being most prevalent in the hangingwall. Graphite is, in general characteristic of the ore host although it may also be found in other carbonaceous parts of the Banded Gneissic Complex (Upadyaya, pers. comm., 1996).
The rock has a well developed schistosity/gneissosity. Graphite occurs as subhedral flakes in association with biotite, feldspar and quartz. Sillimanite is associated with biotite and garnet along well developed foliations. Garnet is generally fractured and accompanies biotite and sillimanite. Quartz, biotite and sillimanite are common inclusions in garnet. Sphalerite and pyrite are the main sulphides seen in the host rocks (Sharma & Singh, 1990).
The margins of the ore zone and of the graphite-mica-garnet-sillimanite schist are occupied by sheared zones which contain a retrograde graphitic-mica schist with a higher graphite content (Upadyaya, pers. comm., 1996).
Within the main host rock unit there are a few bands and zones of calc-silicate and quartz-feldspar-mica rock, with or without garnet. These are barren of ore mineralisation, except for sporadic specks of pyrite (Gandhi, et al., 1984).
Granite gneiss - with varying degrees of migmatisation, is well exposed all along the footwall, and further to the west of the deposit. It is light to mid grey, medium to fine grained, and exhibits alternate layers of dark, lenticular biotite patches and streaks. Major minerals include quartz, elongated feldspar (plagioclase and perthite) and biotite. Rods and needles of sillimanite occur with quartz and feldspar porphyroblasts. Accessory minerals are sericite, muscovite, apatite and zircon. Garnets are present in varying sizes and form an incipient, but conspicuous foliation. Granite gneiss occurs together with thin bands of garnet-biotite gneiss, mylonite, amphibolite and quartzo-feldspathic bands (Gandhi, et al., 1984).
Calc-silicates - occur as hard, compact, well jointed, fine to medium grained granulitic rocks. The principal minerals are diopside, plagioclase, hornblende and grossularite garnet, with minor quartz, K-feldspar and biotite. Accessory minerals include, epidote, apatite, clinozoisite and sphene. Plagioclase and pyroxene (predominantly diopside, but sometimes hypersthene) are present in equal amounts and together constitute around 75% of the rock, while quartz makes up another 20% (Gandhi, et al., 1984; Ranawat & Sharma, 1990; Sharma & Singh, 1990).
Sometimes appreciable calcite is present, such that the rock verges on being an impure marble with a saccharoidal texture. The garnets range in size from 'a few', up to 100 mm in diameter. The calc-silicates are generally green due to the dominance of diopside, and locally they grade into amphibolites. In places there is an incipient mineral banding of leucocratic and melanocratic material. Boudins of various dimensions are seen as are segregations of garnet and pyroxene. At surface they are highly contorted and pitted, exhibiting various minor folds (Gandhi,et al., 1984; Sharma & Singh, 1990).
The calc-silicates are hard and consequently resistant to weathering, forming prominent, bouldery outcrops. They commonly occur as pinch and swell lenses following the overall foliation of the accompanying gneisses (Gandhi, et al., 1984).
Amphibolite - are dark-green to black, granoblastic to foliated. It occurs as bands of varying width in garnet-biotite-sillimanite gneiss and has interfingering relationships with the calc-silicates. The amphibolites are composed of hornblende, plagioclase and garnet with diopside, biotite and quartz. Based on their mineralogy they can be divided into three classes, namely: i). mono-minerallic hornblendite, which exhibits incipient schistosity and occurs in the central parts of the hangingwall in the southern section of the deposit; ii). amphibolite with equal amounts of feldspar and amphibole, occurring largely in the northern part of the deposit and being the result of feldspathic, partly kaolinised, fracture filling veins within the amphibolite; and iii). garnetiferous amphibolite which contains segregations and clusters of garnet that exceed the usual garnet content found in most rocks, and are taken to represent metamorphic differentiation. These occur in a few patches in the southern parts of the orebody (Gandhi,et al., 1984; Sharma & Singh, 1990).
Texturally and structurally there are two types of amphibolite, namely: i). schistose amphibolite which is generally conformable to the gneissosity and parallels the main lithological banding; and ii). more massive amphibolites with columnar jointing that transgress the lithological banding and have been interpreted to represent original intrusives (Upadyaya, pers. comm., 1996).
Garnet-biotite gneiss - a relatively narrow, 10 to 15 m wide band of garnet-biotite gneiss with sillimanite, occurs all along the footwall of the deposit. It is associated with alternate layers of varying width of augen, streaks and lenses of granite gneiss. In addition there are compact and well foliated amphibolites and calc-silicates which are repeated in this interval. As such it resembles a composite gneiss. Pegmatites and aplites also occur as bands, discontinuous veins and as concordant lenses of 'sizeable' dimensions, generally following the dominant foliation (Gandhi,et al., 1984; Sharma & Singh, 1990). This could well be a cataclasite or mylonite.
Pegmatite and Aplite - occur as bands, discontinuous veins and as discordant lenses of "sizeable dimensions", mainly paralleling foliation. They are found both in the hangingwall and footwall. The pegmatites are composed of graphic intergrowths of coarse quartz and feldspar, with very little mica. Garnets occur to varying degrees and in different sizes, up to 120 mm across. Individual pegmatite lenses may be up to 40 m thick locally (Gandhi,et al., 1984).
Mylonite - a series of mylonitic zones are found both within the orebody and particularly within the footwall of the deposit, paralleling the regional foliation. These zones vary from 2 to 40 m in thickness and can be traced for up to 2 km along strike. At least one of the mylonite zones which was sighted about 1 km from the orebody, has been traced parallel to the regional foliation trend for around 80 km. The mylonitic rocks in the vicinity of the ore zone show varying degrees of cataclasis, and are composed of a mixture of the main lithologies described above. The main mylonites comprise a dark grey to black, massive, very fine grained matrix and contain small porphyroblasts of garnet and quartzo-feldspathic material. Fractured garnets are present, accompanied by accessory apatite and sphene. Microscopically they comprise garnet, biotite, quartz, microcline, perthite and oligoclase. Crushing and granulation has been high producing granoblastic textures in the quartz-feldspathic material, while biotite-sillimanite layers produce a schistosity. The groundmass is generally opaque and glassy with black iron oxides (Gandhi, et al., 1984; Upadyaya, pers. comm., 1996). The regional mylonite zone observed during the visit is composed essentially of strongly aligned boudins and porphyroblasts of quartzo-feldspathic material from a few mmÕs to metres long, set in a very fine grained black matrix (Pers. observ., 1996)
Gossan - the orebody has a conspicuous capping of gossan, largely concealed under superficial cover. The outcrops were patchy and variegated grey, white, red, yellow, maroon and black in colour. The gossan was associated with sheared, graphitic mica schist and occurred as massive, vuggy and semi-porous in-situ exposures along the strike of the ore zone. It was generally limonitic, with occasional developments of cellular, spongy boxwork. The weathered/oxidised capping over the fresh sulphides extends to anywhere between 14 and 25 m below the surface (Gandhi, 1990?). Below the upper sections of the gossan there was a transition zone, up to 10 m thick, of partly oxidised and partly fresh sulphides, before reaching the fresh sulphide ore (Gandhi, et al., 1984).
The main components of the gossan are quartz, feldspar, graphite, garnet, sillimanite, limonite and relict sulphides. The bulk of the gossan is made up of limonite, with more sulphides and relict sulphides in the transition zone. In the oxidised zone the contained Zn and Pb are predominantly within sulphate and carbonate phases, followed by oxides and silicates (Gandhi, 1990?).
The ore is hosted by the graphite-mica-garnet-sillimanite schist with which it is generally co-extensive. The exposures of the graphite-mica-garnet-sillimanite schist terminates on a fold closure at the southern end of the ore zone and apparently pinches out with the ore to the north. While there is a sharp contact to the graphite-mica-garnet-sillimanite schist in the footwall, in the hangingwall graphite is still found in the hangingwall schists, gradually diminishing in intensity upwards (Upadyaya, pers. comm., 1996).
Generally within the mine area there are not definite lithological units with a given composition, but rather heterogeneous gneisses and schists that frequently vary gradationally, both in texture and in composition. The orebody and host rocks are more schistose, with sheared outer contacts with the enclosing schists of the adjacent garnet-biotite-sillimanite 'gneiss'. Mylonite zones that are 2 to 40 m thick are found on both sides of the ore, but particularly on the footwall (Upadyaya, pers. comm., 1996), where a 15 to 40 m north thickening mylonite is noted, that may be traced for approximately 2 km (Gandhi, et al., 1984). Near the mylonites there is complex folding. Mylonite zones, 3 to 5 m thick, are also found within the ore producing what is locally called 'disc' ore. Also within the orebody there are oblique shears which influence the changes in thickness of the orebody. In places very high grade zones are found along such shears on the margin of the ore, while in some cases low grade patches with a higher pyrite content are found in the core of thickened intervals. As well as the internal oblique faults within the orebody, there are strike parallel internal shears (Upadyaya, pers. comm., 1996).
Outwards from the ore in the garnet-biotite-sillimanite 'gneiss' the schistose nature of the wall rocks become more gneissic. A relatively narrow, 10 to 15 m wide band of garnet-biotite gneiss with sillimanite, possibly a mylonitised gneiss, occurs all along the footwall of the deposit. It is associated with alternate layers of varying width of augen, streaks and lenses of granite gneiss. Granite gneiss is found in zones in both the hangingwall and footwall of the ore (Upadyaya, pers. comm., 1996).
Within the sequence there are amphibolite lenses which vary in orientation. Those in the footwall are generally parallel to the ore, while those in the hangingwall are oblique to it, striking at approximately 25°, ie. at an angle of around 30° to the orebody. It has been suggested from this that the hangingwall contact of the orebody is a shear zone. Within the immediate hangingwall the garnet-biotite-sillimanite gneiss is more intensely sheared throughout, over a width of around 100 m. In this zone there are boudinaged bands and veins of very coarse grained garnet. Pegmatites are found in both the hangingwall and footwall. They vary from irregular masses to concordant bands, but are less extensive along strike than the orebody. Within and adjacent to the ore there are lensoid bands of calc-silicate (Upadyaya, pers. comm., 1996).
The garnet contained within both the ore zone and the enclosing gneisses is almandine, with no Mn garnets being found (Upadyaya, pers. comm., 1996). The metamorphic assemblage is characterised by garnet, sillimanite, kyanite, amphibole (tremolite and actinolite), diopside, hypersthene, microcline, calcite, graphite and chlorite, implying a grade of almandine-amphibolite to granulite. Garnets have been shattered, and in some places have apparently undergone retrograde modification to biotite and chlorite (Gandhi, et al., 1984).
Structure
The orebody dips to the south-east at 60 to 65° and strikes to the north-east, at around 50° true (Upadyaya, pers. comm., 1996). The schistosity and gneissosity of the enclosing country rocks generally trends from 45 to 65° and dips at around 77° to the south-east. However locally the strike may vary from 28 to 70° while the dips ranges from 50° to vertical. This foliation direction is parallel to the trend of the individual lithologies within the mine area and to the mapped mylonite zones. It is represented by alternating leucocratic quartzo-feldspathic and melanocratic mica bands. Small scale isoclinal folds are noted in amphibolite in the southern part of the orebody, with plunges of 50 to 70° to the NE, while prominent lineations plunge at from 70 to 74° at azimuths of 48 and 132° respectively (Ranawat & Sharma, 1990; Gandhi,et al., 1984)
Ray (1980) have suggested that the orebody area has been subjected to three periods of deformation, namely: i). an initial isoclinal folding with a variable plunge and axial plane that produced WNW-ESE trending folds; ii). a further, subsequent isoclinal folding which folded the S1 axial plane about a NE-SW axis; and iii). a weak, local phase of upright, steeply plunging folding. He claims that the resultant structure was an upright doubly plunging isoclinal synform, with a plunge on the southern closure of 20° to the NE, and on the northern closure of 40° to the SW. However on the mine visit it was indicated that the structure may represent a single sheared limb, with a southern plunging closure as indicated above. The southern termination, which has been confirmed by two drill holes, may not represent a major closure, but a local parasitic fold adjacent to a hangingwall shear zone. No evidence is apparently available to confirm a northern closure. The northern margin, where the ore thins but increases substantially in grade, could equally represent the truncation of the orebody by an adjacent acute shear. There is no indication of fold repetition of the ore in drilling, nor of any axial zone and closure within the orebody. The orebody appears to continue at depth, accompanied by thinning, as shown on the attached drill sections (Upadyaya, pers. comm., 1996).
Within the orebody it is possible to see substantial faces in which small to large blocks of ore up to several metres across can be seen to be randomly oriented within the main massive to semi-massive ore zone, indicating strong structural disruption.
Mineralisation
The host to the economic sulphide mineralisation is graphite-mica-sillimanite gneiss/schist which has a sharp contact with the footwall and hangingwall rocks. The ore is banded and varies from massive fine to medium grained, to disseminated sulphides, but overall averages 35 to 55% sulphides. The major sulphide ore minerals are sphalerite and galena, with a gangue of pyrite, pyrrhotite, arsenopyrite and various sulpho-salts. Rare chalcopyrite has been identified. There is little to no magnetite within the ore. The ore includes numerous inclusions of sub-rounded porphyroblasts of feldspar, quartz and quartzo-feldspathic material, commonly set in a fine grained matrix of sphalerite, pyrrhotite, pyrite and silicates (Höller & Gandhi, 1995; Ranawat & Sharman, 1990; Mukherjee, et al., 1991).
Graphite is also a common gangue mineral, constituting 6 to 10% of the ore by volume, locally up to 20%. It is present as shards and flakes, and within fractures as a fine filling encircling other gangue and sulphide minerals. Sphalerite is the dominant sulphide within the orebody, although small sections may be dominated by either galena or pyrrhotite (Höller & Gandhi, 1995; Mukherjee, et al., 1991).
The orebody occurs principally as a single sulphide body, although a minor string of galena rich lenses up to 2 m thick are also found 8 to 15 m into the hangingwall in some parts of the mine (Upadyaya, pers. comm., 1996).
Sulphides are present in the following forms: i). as bands with a sharp contact with the adjacent host rock; ii). as disseminations filling inter-granular and intra-granular spaces; iii). stringers along foliation planes; iv). patches replacing the host rock; v). very fine intergrowths of sulphide and gangue rock; and vi). traces of sulphides filling very fine cracks within the host rock (Sharma
& Singh, 1990). Most of the ore sighted during the visit was massive to semi-massive and medium grained (0.5 to 2 mm), with no banding.
In general the ore exhibits a metamorphic fabric of granular and annealed textures between two minerals or amongst different grains of the same mineral. The sulphosalts freibergite, argentian parachute and miargyrite occur as inclusions and fine veins within sphalerite, sometimes in close association with pyrite. Primary mineral banding is very rare. The sulphides have been recrystallised to produce aggregates of sulphides with grain sizes exceeding 3 mm in places, with galena, sphalerite and pyrrhotite having been remobilised. The quartz and feldspar gangue exhibits numerous cracks which are filled with sulphides and sulpho-salts. Sandwich like intergrowths of sulphides with graphite and phyllosilicates are very common. Ball structures have been observed, composed of rolled porphyroclasts of silicates and sulphides in a sulphide matrix. Rare Cr-V oxides, gahnite and pyrophanite are also recorded (Höller & Gandhi, 1995; Mukherjee, et al., 1991). These textures and structures are characteristic of ore that has been subjected to structural translation, remobilisation and recrystallisation.
A study of the ore did not reveal any zonation of sulphides within the orebody in detail, although the Zn:Pb:Fe ratio can vary within metres (Höller & Gandhi, 1995). There is however, a tendency for there to be richer sections that are 5 to 7 m thick in both the hangingwall and footwall. These are associated with retrograde shearing on the margins of the orebody, and have a gangue of chlorite and enhanced graphite. This produces a friable ore. The high grade hangingwall band is the thicker. These richer bands are mainly on the central to southern parts of the orebody. The lead grade also tends to be higher in the hangingwall sections of the orebody, with associated coarse grained galena. The sheared margins of the orebody are bounded by barren schist to gneiss which generally contain <100 ppm Pb and Zn (Upadyaya, pers. comm., 1996).
Laterally the thinner northern end of the orebody have the highest grades, carrying up to 20% Zn and 2.5% Pb, but are lower in total Fe. In contrast, in the southern sections there are generally lower grades, with higher Fe levels, lower Pb+Zn, and some internal low grade blocks. The largest of these low grade pods is 12 to 25 m thick, centred on 300 mS, and only contains 3 to 4% Zn+Pb. It is composed of granular gangue minerals, with galena, sphalerite and negligible associated pyrite. The central sections of the orebody are generally of average grade. Galena rich bands up to 2 m thick are localised in parts of the orebody, mainly within 20 to 30 m of the hangingwall. Pyrrhotite is more strongly developed between 200 and 500 mS (Upadyaya, pers. comm., 1996; Gandhi, et al., 1984).
The occurrence of the main sulphides can be summarised as follows:
Sphalerite - is by far the dominant sulphide and occurs as fine to coarse grained aggregates in close association with galena, pyrrhotite and pyrite, and with long flakes of graphite. The sphalerite has a variety of colours, ranging from brownish-black, to black, to light-brown and yellowish-brown. Aggregates of sphalerite commonly contain inclusions of galena and graphite, as well as exsolved blebs of pyrrhotite. Chalcopyrite is present as exsolved grains in a ground mass of sphalerite, while greenockite is also present as minute inclusions and margin fillings. The predominant form of sphalerite is the black iron rich variety marmatite, averaging 11.5% Fe, 0.5% Mn, 0.3% Cd (Höller & Gandhi, 1995; Sharma & Singh, 1990).
Galena - occurs in the main ore zone as fine to medium disseminations and as veinlets. It is also present as a fine grained matrix, cementing sub-rounded to angular gangue minerals of various sizes, and as coarse grained crystals which deform the adjacent foliations. It is found as coarse grained aggregates in close association with sphalerite and pyrrhotite, or encloses sub-rounded gangue minerals and other sulphides, such as tennantite-tetrahedrite. Remobilisation of galena along fissures and the cleavage of gangue minerals is common. Minor constituents, such as Bi, Sb, Ag and Se are below detection limits. Patches of tennantite-tetrahedrite are noticeable in the hangingwall calc-silicate rocks associated with galena mineralisation (Höller & Gandhi, 1995; Sharma & Singh, 1990).
Pyrrhotite - is erratically distributed through the orebody, but forms coarse aggregates of polygonal grains, which display metamorphic crystallisation. It also occurs as fine grained aggregates intergrown with other sulphides, particularly sphalerite, pyrite and coarse grained galena, or as exsolved inclusions in sphalerite. Pyrrhotite grains are often incipiently decomposed to a granular mass of pyrite and marcasite. It is invariably relatively pure with no more than traces of Ni and Co (Höller & Gandhi, 1995; Sharma & Singh, 1990).
Pyrite - forms as granular aggregates of polygonal crystals up to 5 mm across, or as veinlets, but may also be intergrown with pyrrhotite or marcasite. Some pyrite has small inclusions of sphalerite, while others are 'eaten' by sphalerite with 'tooth print' shaped boundaries. Large porphyroblasts show brittle fractures filled with other sulphides. Porphyroblasts of pyrite are also found within cataclastic sphalerite, suggesting late formation after cataclasis (Höller & Gandhi, 1995; Sharma & Singh, 1990). Pyrite is also found as small specks in the hangingwall rocks, particularly the calc-silicates and amphibolites (Upadyaya, pers. comm., 1996).
Arsenopyrite - is a common minor constituent and forms subhedral to euhedral crystals up to 3 mm across that are occasionally flattened parallel to the foliation of highly deformed samples. Sometimes crystals are bent and show plastic deformation. Large crystals may enclose a core of löllingite. The arsenopyrite contains up to 0.5% Ni and 0.45% Co (Höller & Gandhi, 1995; Sharma & Singh, 1990).
Chalcopyrite - is a minor constituent occurring as grains up to 100 µm across and as disseminated anhedral grains interstitial to the dominant iron sulphide (Höller & Gandhi, 1995).
Greenockite - forms as anhedral grains <20 µm across within galena and is commonly associated with boulangerite and freibergite (Höller & Gandhi, 1995).
Graphite - is the most common gangue constituent associated with the ore and may constitute up to 5 to 10% by volume, occurring as flakes and shards filling fractures and encircling other gangue and sulphide minerals. It also occurs as inclusions within the sulphides.
The sulphide minerals comprise around 40 to 55% of the ore.
The most recent source geological information used to prepare this decription was dated: 1996.
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.
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Selected References:
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Holler W and Ghandi S M, 1995 - Silver-bearing sulfosalts from the metamorphosed Rampura-Agucha Zn-Pb-(Ag) deposit, Rajasthan, India: in The Canadian Mineralogist v.33 pp. 1047-1057
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Holler W, Touret J L R, Stumpfl E F, 1996 - Retrograde fluid evolution at the Rampura Agucha Pb-Zn-(Ag) deposit, Rajasthan, India : in Mineralium Deposita v31 pp 163 - 171
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Mishra B and Bernhardt H-J, 2009 - Metamorphism, graphite crystallinity, and sulfide anatexis of the Rampura–Agucha massive sulfide deposit, northwestern India: in Mineralium Deposita v.44 pp. 183-204
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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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