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Research Article
 

Petrochemistry of the Reduced, Ilmenite-Series Granitoid Intrusion Related to the Hired Gold-Tin Prospect (Basiran), Eastern Iran



M.H. Karimpour, C.R. Stern, A. Malekzadeh Shafaroudi, M.R. Hidarian and A. Mazaheri
 
ABSTRACT

Doing research, two suites of Oligocene-Miocene granitoids, one relatively oxidized (magnetite-series) and the other relatively reduced (ilmenite-series), were identified at Hired, Eastern Iran. Since Au-Sn mineralization is associated only with the relatively reduced ilmenite-series suite. It became interested to study the petrochemistry and petrophysics of these intrusive rocks. The magnetic susceptibility of the magnetite-series granitoids is greater than 300 x10-5 SI. This suite includes meta-aluminous, medium-K to high-K series gabbros to diorites containing magnetite, hornblende and biotite. The magnetic susceptibility of the ilmenite-series granitoids are less than 60 x10-5 SI. This suite includes meta-aluminous, high-K to shoshonitic diorites to granites, containing, biotite, muscovite and tourmaline. Both the ilmenite and magnetite series suites are strongly enriched in large ion lithophile elements (LILEs = K, Th, Rb, Ba) and depleted in high field strength elements (HFSE = Nb, Sr, Ti, Hf). Chondrite-normalized Rare Earth Element (REE) plots indicate strong enrichments of light relative to heavy REE, with (La/Yb)N between 7-24. Ilmenite suite granitoids have pronounced negative europium anomalies. Stockwork mineralization is found within and nearby the relatively reduced ilmenite-series granites. Based on their mineral assemblages (arsenopyrite, pyrrhotite, tourmaline, pyrite, gold and quartz), the ore-bearing fluids that generated these stockwork veins was also reduced. This and the spatial relationship of mineralization with the ilmenite suite granitoids, indicates that the ore fluids originated from reduced granitoid magmas. Hired Au-Sn deposit is a reduced-intrusion related gold system.

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M.H. Karimpour, C.R. Stern, A. Malekzadeh Shafaroudi, M.R. Hidarian and A. Mazaheri, 2009. Petrochemistry of the Reduced, Ilmenite-Series Granitoid Intrusion Related to the Hired Gold-Tin Prospect (Basiran), Eastern Iran. Journal of Applied Sciences, 9: 226-236.

DOI: 10.3923/jas.2009.226.236

URL: https://scialert.net/abstract/?doi=jas.2009.226.236

INTRODUCTION

The Hired Au-Sn prospecting is located 150 km south of Birjand (Eastern Iran), between 59°08’E to 59° 15’E and 31°59’N to 31°54’N (Fig. 1). The Geological Survey of Iran carried out a preliminary mineral exploration project in the area looking for gold. With this research we identified two distinct suites of granitoids rocks in the area, one with relatively oxidized with high magnetic susceptibility (magnetite-series) and the other relatively reduced with low magnetic susceptibility (ilmenite-series). At Hired, gold is associated with ilmenite series.

Gold deposits related to intrusive rocks have been called porphyry gold deposits, intrusion-related stockwork-disseminated deposits (Sillitoe, 1997, 2002; Sillitoe and Thompson, 1998), plutonic-related gold deposits (McCoy et al., 1997) and intrusion-related gold deposits (Thompson et al., 1999). Lang et al. (2000) and Lange and Baker (2001) preferred the term intrusion-related gold systems.

Several style of mineralization such as stockwork, skarn, vein and replacements were recognized in the area. Stockwork mineralization and alteration is associated specifically with the reduced, low magnetic susceptibility ilmenite-series granitoids. Further research and exploration revealed that the area also has potential for Sn. This study presents the results of further field and petrochemical study of the igneous rocks and associated alteration and mineralization in the Hired prospect area.

MATERIALS AND METHODS

This research was started in February 2006 with a grant from Geological Survey of Iran and followed with grant from Ferdowsi University of Mashhad in February 2008. The Hired Au-Sn prospectin is located 150 km south of Birjand (Eastern Iran), between 59°08’E to 59° 15’E and 31°59’N to 31°54’N (Fig. 1).

Detail field study carried in an area approximately 30 km2 such as:

Fig. 1: Location of Hired gold deposit

Geology map at scale of 1:5000
Alteration and mineralization maps at scale of 1:5000
Rock geochemical exploration
Core logging
Ground magnetic geophysical exploration

Laboratory study

Petrography and mineralography
Major oxides were analyzed using XRF at Ferdowsi University of Mashhad, Iran
Trace and REE were analyzed using ICP-Ms at University of Colorado Boulder, USA
Magnetic susceptibility was measured using GMS2 Sintrex meter having accuracy of 1x10-5 SI
Sn, Au, Cu, As, Sb…were analyzed in Canada

RESULTS

Magnetism: Ishihara (1977) classified granitoids rocks based on magnetic properties into ilmenite and magnetite series. Ilmenite series have magnetic susceptibility less than 80x10-5 SI and magnetite series have magnetic susceptibility bigger than 80x10-5. Magnetic susceptibility of over 100 intrusive rocks from the Hired study area was measured. Based on the magnetic susceptibility, intrusive rocks were classified into ilmenite series and magnetite series (Table 1). On Fig. 2, both series and associated rock types are shown.

Based on field observation, petrography study and this magnetic susceptibility measurement, two distinct series of Oligocene-Miocene granitoids (magnetite and ilmenite-series) were identified in the study area (Fig. 3). Magnetite-series granitoids are exposed in the northeast part of the study area (Fig. 3). The ilmenite-series granitoids are exposed in the central and western part of the area (Fig. 3).

Table 1: Magnetic susceptibility of Hired granitoids

Fig. 2: Classification of Hired intrusive rocks into ilmenite and magnetite series

Fig. 3: Geological map of Hired Gold prospecting area

By plotting the location of intrusive rocks on the aeromagnetic maps, it is clear that all of the magnetic series corresponded with the areas of high magnetism and ilmenite series with area of low magnetism (Fig. 4).

Petrography: The oldest rocks exposed in the study area are Jurassic shales and sandstones (Fig. 3). Cretaceous rocks are conglomerates, sandstones, limestones and tuffs. Igneous rocks generated during the Paleocene-Eocene are mainly andesitic in composition (Fig. 3). During Neogene time, volcanic activity changed and rocks of basaltic composition were formed.

The magnetite-series suite consists of at least four types of intrusive: gabbro, biotite hornblende diorite, biotite hornblende monzodiorite and biotite hornblende quartz monzonite. The gabbro contains 70-75% plagioclase, 20-25% pyroxene, 0.5-1% quartz and alkali feldspar and 0.5% opaques. Biotite hornblende diorite has the largest area of exposure (Fig. 3). It contains 60-65% plagioclase, 10% k-feldspar, 5% quartz, 7-10% biotite and less than 7% amphibole. Accessories minerals are apatite, zircon and magnetite. Secondary minerals are chlorite and calcite. Biotite hornblende monzodiorite is exposure in the central part of the map. It has porphyritic texture with 25-30% phenocrysts. The phenocrysts contain 25% plagioclase, 4% hornblende and 3% biotite. Groundmass contains plagioclase, k-feldspar, biotite, hornblende, quartz and magnetite. Secondary minerals are chlorite and calcite. Biotite hornblende quartz monzonite is exposed in the western part of the map area (Fig. 3). It contains 35% plagioclase, 40-45% k-feldspar, 10-5% quartz, 7-10% hornblende and less than 3% biotite. Accessories minerals are apatite, zircon and magnetite. Secondary minerals are chlorite and calcite.

Fig. 4: Aeromagnetic map of Hired gold prospecting area and the exposure of intrusive

Several intrusive rocks belonging to the ilmenite-series granitoids occur in the area. Four of them are shown on the map (Fig. 3). These are granite, biotite granite, biotite-hornblende quartz monzonite and hornblende diorite. Granite has the largest exposure in the central part of the map area. It contains 30-35% k-feldspar, 40-45% albite and 25% quartz. Accessories minerals are apatite, zircon. Secondary minerals are chlorite, sericite, tourmaline and calcite. Biotite-hornblende granite porphyry has porphyry texture with aplitic groundmass. It contains 60-65% feldspar highly altered, 20-25% quartz and less than 1% biotite and hornblende totally altered. Secondary minerals are chlorite, sericite, tourmaline and quartz. Biotite-hornblende quartz monzonite has exposure on the west side of the map area. It contains 35-40% plagioclase, 25-30% k-feldspar, 15% quartz, 2-3% biotite and 7% hornblende. Secondary minerals are chlorite, quartz, tourmaline and calcite. Hornblende diorite has small exposure on the east side of the map. It contains 75% plagioclase, 12% k-feldspar, 5% quartz and 10% hornblende. Secondary minerals are chlorite, quartz, tourmaline and calcite.

Alteration and Mineralization: Both alteration and mineralization maps at scale of 1:5000 were produced (Fig. 5). Four style of mineralization, including stockwork, skarn, vein and dissemintated replacement, were identified. Stockwork mineralization is present within and near the ilmenite series granite porphyry (Fig. 5), in the central part of the map Target No-I. Stockwork veins consist of different minerals such as tourmaline, quartz, quartz-sulfides, quartz-calcite and quartz-chlorite. The width of veinlets varies between 1 to 20 mm. Mineral paragnesis of the stockwork veins are plotted in Fig. 6. Arsenopyrite, pyrrhotite, galena, sphalerite ± chalcopyrite are the main sulfide minerals.

Fig. 5: Alteration and mineralization map of hired gold prospecting area

Four types of alteration are related to the stockwork veins. These include propylitic, tourmaline-sericite, chlorite-tourmaline and tourmaline-sericite-quartz. Propylitic alteration dominates over a large area. It consists of chlorite and minor calcite. Tourmaline-sericite-quartz alteration is found most closely associated with stockwork mineralization (Fig. 5). Based on mineral paragnesis and alteration the hydrothermal fluid that produced these veins and the associated alteration was reduced, with low sulfur and high concentrations of As, B, Si, Au, Sn, Sb.

Geochemical exploration: Rock geochemical exploration was carried out both on surface and drill core. The chemical composition of some elements is Au = 5-5500 ppb, Cu = 40-3500 ppm, Sn = 4-550 ppm, As = 300- >10000 ppm, Sb = 3-1300 ppm, Pb = 50-2500 ppm and Zn = 60-2500 ppm. As is very high and is present as arsenopyrite. The Au, As, Pb and Zn content of drill hole DDH-B7 (depth 100 m) from within the zone of stockwork mineralization is shown in Fig. 7. Au content of DDH-B7 begins to increase (Au = 5500 ppb) at depth of 55 m. Pb and Zn content of DDH-B7 begins to increase at depth of about 70 m (Fig. 7). The Sn content DDH-B7 increases at depth up to 550 ppm. High Au, Pb, Zn formed a halo at the top of the Sn mineralized system at Hired. The Sn must be much higher at depth within the area samples by DDH-B7.

Fig. 6: Mineral paragnesis of hired gold prospecting area

Petrology: Representative rocks from the ilmenite and magnetite series of granitoids were analyzed for major and trace elements (Table 2). To classified these rocks, the chemical composition of both series are plotted in (Middlemost, 1994, Fig. 8). The ilmenite-series plotted in the field of granite, granodiorite and quartz monzodiorite. The magnetite-series suite plotted in the field of granodiorite, tonalite, quartz diorite and gabbro (Fig. 8). Aluminum Saturation Index (ASI) value for both ilmenite and magnetite series are less than 1, therefore they are both meta-aluminous (Fig. 9). SiO2 verses K2O plot (Peccerillo and Taylor, 1976) indicates that ilmenite series are high K2O to Shoshonite and magnetite series are medium to high K2O (Fig. 10).

Fig. 7: Au, As, Pb and Zn content of DDH-B7 of Hired

Table 2a: Major and trace elements analysis of representative rocks from different granitoids (XRF)

Table 2b: CIPW-Bi-Hlb normative mineral

Fig. 8: Hired intrusive rocks are plotted in Middlemost (1994) for classification

Fig. 9: Hired intrusive rocks plotted in filed of met-aluminous

Fig. 10: Plot of SiO2 versus K2O

Fig. 11: Ilmenite series have higher U and Th

Fig. 12: Sn content of ilmenite series is much higher than magnetite series

U versus Th show that ilmenite series have higher U and Th, U = 2-9 ppm and Th = 15-35 ppm (Fig. 10). Magnetite series have lower U and Th content (Fig. 11). Sn content of ilmenite series varies between 2-15 ppm, but in the magnetite series Sn is less than 2 ppm (Fig. 12).

Representative rocks from both magnetite and ilmenite suites were analyzed for rare earth and trace elements using ICP-MS at the University of Colorado-Boulder (Table 3). MORB-normalized trace-element diagrams (Fig. 13) indicates that both ilmenite and magnetite suites are strongly enriched in large ion lithophile elements (LILEs = K, Th, Rb, Ba) and depleted in high field strength elements (HFSE = Nb, Sr, Ti, Hf) (Fig. 13). Chondrite-normalized REE plots indicate strong enrichments of LREE (Fig. 14). In comparison with magnetite suite, the ilmenite series granitoids show more enrichment of LREE (Fig. 14). The magnetite suites generally have no obvious europium anomalies, whereas ilmenite-series granitoids have pronounced negative europium anomalies (Fig. 14).

Fig. 13: Spider diagram Hired intrusive/MORB (Circle = ilmenite series, triangle = Ilmenite series)

Fig. 14: REE normalized with respect to chondrite

Table 3: Rare earth elements analysis of representative rocks (ICP-MS)

On the trace-element discrimination diagrams of Pearce et al. (1984), Y+Nb versus Rb both ilmenite and magnetite suites plotted in the field of volcanic arc (Fig. 15a) but on Ta+Yb versus Rb, magnetite suites plotted in the field of volcanic arcs but ilmenite suites overlaps both the syn-collisional and volcanic-arc fields (Fig. 15b).

DISCUSSION

Gold deposits related to intrusive rocks have been called porphyry gold deposits, intrusion-related stockwork-disseminated deposits (Sillitoe, 1997, 2002; Sillitoe and Thompson, 1998), plutonic-related gold deposits (McCoy et al., 1997) and intrusion-related gold deposits (Thompson et al., 1999). Lang et al. (2000) and Lange and Baker (2001) preferred the term intrusion-related gold systems.

Iron-oxides Cu-Au (IOCG) (Williams et al., 2005; Sillitoe, 2003; Barton, 2001; Haynes, 2000; Hitzman, 2000) deposits are reported mainly in subduction related setting and some in rifted environment. The source rocks are oxidized to highly oxidized (I-type, magnetite series), metaluminous, mainly intermediate in composition and medium to high-K series.

Porphyry Cu-Au or porphyry Au deposits are reported mainly in subduction related setting. Their source rock are I-type (oxidized, Magnetite series), calc-alkaline to alkaline, metaluminous, high-K series to Shoshonite.

According to Lang and Baker (2001), The principal discussions (Craig et al., 2005; Sillitoe, 2002; Lang et al., 1997; McCoy et al., 1997; Thompson et al., 1999; Marsh et al., 2003; Lang et al., 2000; Gordey et al., 2004) suggested that there are several features common to most intrusion-related gold deposits and provinces, including: (1) metaluminous, subalkalic intrusions of intermediate to felsic composition that lie near the boundary between ilmenite and magnetite series; (2) carbonic hydrothermal fluids; (3) a metal assemblage that variably combines gold with elevated Bi, W, As, Mo, Te and/or Sb and low concentrations of base metals; (4) a low sulfide mineral content, mostly <5vol%, with a reduced ore mineral assemblage that typically comprises arsenopyrite, pyrrhotite and pyrite and which lacks magnetite or hematite and (5) spatially restricted, commonly weak hydrothermal alteration, except in systems formed at the shallowest depths spanned by these deposits.

Comparison of Hired Au-Sn prospecting area with the above features indicates important differences, which are: (1) Au-Sn mineralization is only associated with reduced intrusive (ilmenite suites), (2) boron-carbonic hydrothermal fluids (Alteration), (3) metal assemblage are Au, As, Sn, Sb, with very low-W and (4) oxidized intrusive rocks (magnetite suites) did not have any mineralization.

Gold deposits associated with reduced type ilmenite granitoid suites are shown in Table 4. Tungsten is very common in most of them except for Hired. At Hired Sn, is very important. Arsenopyrite and pyrrhotite are distinctive minerals in all of them. Style of mineralization varies from sheeted veins, disseminated, breccia and stockwork.

Table 4: Gold deposits associated with the ilmenite series (reduced type) intrusive rocks

Fig. 15: Tectonic setting of (a) magnetite and (b) ilmenite suites (Pearce et al., 1984). Circle ilmenite suites

Fig. 16: Model shows the source and chemical composition of the ore bearing fluid for Hired Au-Sn deposit

CONCLUSION

Based on the magnetic susceptibility and petrography study at Hired there are two types of intrusive rocks: Ilmenite series and magnetite series. Both ilmenite and magnetite suites were emplaced during Oligo-Miocene time. Based on field observation (contact such as chilled margins, crosscutting, magnetite series are being altered from magmatic fluid was associated with ilmenite series) the ilmenite suites are younger. Au-Sn is associated with the ilmenite suites (Fig. 16). Mineral paragnesis pyrrhotite arsenopyrite (absence of magnetite and hematite) indicate that the fluid which these mineral were formed had reduced character (Fig. 16). Based on types of alteration and mineral paragnesis the fluid originated from the reduced granite (ilmenite suites) was enriched in As, B, Au, Sn, Sb, Pb and Zn.

High Au, Pb, Zn formed a halo at a top of Sn mineralized system at Hired. The Sn must be much higher at depth within area of DDH-B7.

ACKNOWLEDGMENTS

Research began with a grant from geological Survey of Iran, grant No. 125 (February 2006) to study the geophysical properties of the prospecting area. The petrochemistry of the area carried based on a grant from Ferdowsi University of Mashhad, Iran, grant No. p/1727- date 16-February-2008.

REFERENCES
Baker, E.M. and F.J. Tullemans, 1990. Kidston Gold Deposit. In: Geology of the Mineral Deposits of Australia and Papua New Guinea, Hughes F.E. (Ed.). The AusIMM, Melbourne, Mono, pp: 1461-1465.

Barton, M.D., 2001. Sodic alteration and Fe-oxide-rich hydrothermal systems. GSA Annual Meeting, November 5-8, Boston, Massachusetts.

Craig, J.R., J.L. Mair, R.G. Goldfarb and D.I. Groves, 2005. Source and redox controls on metallogenic variations in intrusion-related ore systems. Tombstone-Tungsten Belt, Yukon Territory, Canada. Trans. Royal Soc. Edinburgh Earth Sci., 95: 339-356.
Direct Link  |  

Gordey, S.P., J.J. Ryan and R.B. Cocking, 2004. Geology, Stewart River Area (Parts of 115 N/1,2,7,8 and 115-O/2-12), Yukon Territory. U.S. Geological Survey Open-File Report 2004–1451. http://pubs.usgs.gov/of/2004/1451/gordey/index.html.

Haynes, D.W., 2000. Iron Oxide Copper Gold Deposits: Their Position in the Ore Deposit Spectrum and Modes of Origin. In: Hydrothermal Iron Oxide Copper-Gold and Related Deposits: A Global Perspective, Porter, T.M. (Ed.). Australian Mineral Foundation, Adelaide, pp: 71-90.

Hitzman, M.W., 2000. Iron Oxide-Cu-Au Deposits: What, Where, When, and Why. In: Hydrothermal Iron Oxide Copper-Gold And Related Deposits: A Global Perspective, Porter, T.M. (Ed.). Australian Mineral Foundation, Adelaide, pp: 9-25.

Ishihara, S., 1977. The magnetite- series and ilmenite- series granitic rocks. Mining Geology, 27: 293-305.
Direct Link  |  

Lang, J.R. and T. Baker, 2001. Intrusion-related gold systems: The present level of understanding. Mineralum Deposita, 36: 477-489.
CrossRef  |  

Lang, J.R., T. Baker, C.J.R. Hart and J.K. Mortensen, 2000. An exploration model for intrusion-related gold systems. Soc. Econ. Geol. News, 40: 7-75.

Long, K., S. Ludington, E. Du Bray, O. Andrea -Ramos and E. McKee, 1992. Geology and mineral deposits of the La Joya district, Bolivia. SEG. Newsletter, 10: 13-16.
Direct Link  |  

Marsh, E.E., R.J. Goldfarb, C.J.R Hart and C.A. Johnson, 2003. Geology and geochemistry of the Clear Creek intrusion-related gold occurrences, Tintina Gold Province, Yukon, Canada. Can. J. Earth Sci., 40: 681-699.
CrossRef  |  Direct Link  |  

McCoy, D.T., R.J. Newberry, P.W. Layer, J.J. DiMarchi and A. Bakke et al., 1997. Plutonic Related Gold Deposits Of Interior Alaska. In: Ore Deposits of Alaska. Goldfarb, R.J. and L.D. Miller (Eds.). Society of Economic Geology Monograph, Monograph, pp: 151-159.

Middlemost, E.A.K., 1994. Naming materials in the magma igneous rock system. Earth Sci. Rev., 37: 215-224.
Direct Link  |  

Mustard, R., T. Ulrich, V.S. Kamenetsky and T. Mernagh, 2006. Gold and metal enrichment in natural granitic melts during fractional crystallization. Geol. Soc. Am., 34: 85-88.
CrossRef  |  

Pearce, J.A., N.B.W. Harris and A.G. Tindle, 1984. Trace element discrimination diagrams for the tectonic interpretation of granitic rocks. J. Petrol., 25: 956-983.
CrossRef  |  Direct Link  |  

Peccerillo, A. and S.R. Taylor 1976. Geochemistry of eocene calc-alkaline volcanic rocks from the Kastamonu area, Northern Turkey. Contribut. Mineral. Petrol., 58: 63-81.
CrossRef  |  Direct Link  |  

Sillitoe, R.H. and J.F.H. Thompson, 1998. Intrusion-related vein gold deposits: Types, tectono-magmatic settings and difficulties of distinction from orogenic gold deposits. Resour. Geol., 48: 237-250.
Direct Link  |  

Sillitoe, R.H., 1997. Characteristics and controls of the largest porphyry copperâ€`gold and epithermal gold deposits in the circum- Pacific region. Aust. J. Earth Sci., 44: 373-388.
CrossRef  |  Direct Link  |  

Sillitoe, R.H., 2002. Some metallogenic features of gold and copper deposits related to alkaline rocks and consequences for exploration. Mineralium Deposita, 37: 4-13.
CrossRef  |  Direct Link  |  

Sillitoe, R.H., 2003. Iron oxide-copper-gold deposits: An andean view. Mineralium Deposita, 38: 787-812.
CrossRef  |  

Spiering, E.D., L.R. Pevida, C. Maldonado, S. González and J. Garcia et al., 2000. The gold belts of western Asturias and Galicia (NW Spain). J. Geochem. Explorat., 71: 89-101.
Direct Link  |  

Thompson, J.F.H., R.H. Sillitoe, T. Baker, J.R. Lang and J.K. Mortensen, 1999. Intrusion- related gold deposits associated with tungsten-tin provinces. Mineralium Deposita, 34: 323-334.
CrossRef  |  

Williams, P.J., M.D. Barton, D.A. Johnson, L. Fontbote and A. De Haller et al., 2005. Iron Oxide Copper-Gold Deposits: Geology, Space-Time Distribution and Possible Modes of Origin. In: Economic Geology 100th Anniversary, Hedenquist, J.W., J.F.H. Thompdon, R.J. Goldfarb and J.P. Richards (Eds.). SEG, Denver, pp: 371-405.

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