Epigenetic BIF-hosted gold lodes at the Abu Marawat area,Eastern Desert,Egypt: Integrated mineralogical,structural control and fluid inclusion studies

Abstract

Numerous massive and sheared, milky quartz veins cut a sequence of Neoproterozoic island arc metavolcanic/volcaniclastic rocks and related banded iron formation (BIF) at the Abu Marawat area, central Eastern Desert of Egypt. Sulphide-bearing quartz veins and related hydrothermal breccia masses display a range of textures including sheared, boudinaged and recrystallised quartz, quartz with open space filling and microbreccia, implying a complex history of crack-seal processes characterising the relationship between mineral deposition and a major N–S-trending shear zone, during a late brittle–ductile deformation event that affected the area at ∼550 Ma. Gold-base metal mineralisation is associated with brecciation and fracturing of the iron ore bands, close to silicified shears and related quartz veins. The auriferous quartz lodes are characterised by the occurrence of visible pyrite-chalcopyrite±pyrrhotite±sphalerite±galena mineralisation. Gold is refractory in pyrite and chalcopyrite, but rare visible gold/electrum and telluride specks were observed in a few samples. Hydrothermal alteration includes selectively pervasive silicification, pyritisation, sericitisation, carbonatisation that are confined to a delicate set of veins and altered shears, and a more widespread propylitic alteration assemblage (quartz+||chlorite+pyrite+calcite±epidote). The predominance of hydrated silicate phases (i.e. chlorite and sericite) within and adjacent to the shear zones points toward fixation of H₂O during the shear zone development, while CO₂ was consumed to form carbonate in halos around the chlorite-dominated zones, leading to variations in the H₂O/CO₂ ratio of the ore fluid with progression of the hydrothermal alteration.

Ore textures, including hydrothermal quartz intimately associated with replacement of magnetite by pyrite, suggest the introduction of ore fluids via epigenetic conduits into the iron-rich wallrocks. Fluid inclusion textural and microthermometric studies indicate heterogeneous trapping of a low-salinity (1·4–6·7 wt-% eq. NaCl) aqueous solution that coexisted with a carbonic fluid. Evidence for fluid immiscibility during ore formation includes variable liquid/vapour ratios in inclusions along individual trails and bulk inclusion homogenisation into liquid and occasionally to vapour at comparable temperatures. The trapping conditions of intragranular aqueous-carbonic inclusions approximate 264–378°C at 700–1300 bar. Similar temperature estimates have been obtained from Al-in-chlorite geothermometry of chlorite associated with sulphides in the mineralised quartz veins. Fracturing enhanced fluid circulation through the wallrock and related BIF, allowing reaction of the S-bearing ore fluid with iron oxides. This caused formation of pyrite, a rise in Eh and concomitant Au precipitation, which was enhanced by fluid immiscibility as H₂S partitioned preferentially into the carbonic phase. The ore fluids have probably originated from felsite intrusions, whereas Abu Marawat gold deposit and the post-Hammamat felsites is assumed in view of their communal relationship with the N–S fault/shear trend and high geothermal gradient calculated from the fluid inclusion data.

Keywords

ABU MARAWAT BIF SHEAR ZONE GOLD MINERALISATION EASTERN DESERT EGYPT

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References

Abdel Tawab

M. M.

and Zaki

M. A.

: ‘Geochemical exploration, Abu Marawat gold mine', Internal Report, Egyptian Geological Survey, Cairo, Egpyt, 1987, 114.

Akawy

: ‘Fault characterization and paleostress analysis in the Precambrian rocks west of the Meatiq Dome, Central Eastern Desert, Egypt', Neues Jahrbuch für Geologie und Paliiontologie, Abhandlungen, 2003, 228, 1–35.

Akawy

: ‘Geometry and texture of quartz veins in Wadi Atalla area, Central Eastern Desert, Egypt', J. Afr. Earth Set, 2007, 47, 73–87.

Aly

N. A.

, Hegazy

H. A.

and El Tigrawy

A. A.

: ‘Geology and petrochemistry of the arc volcanics in the Semna area, southwest of Safaga, Egypt', Bull. Fac. Set, Assiut Univ., 1991, 20, 61–78.

Andrianjakavah

, Salvi

, Béziat

, Guillaume

, Rakotondrazafy

and Moine

: ‘Textural and fluid inclusion constraints on the origin of the banded-iron-formation-hosted gold deposits at Maevatanana, central Madagascar', Miner. Depos., 2007, 42, (4), 385–398.

Armanious

L. K.

: ‘Gabel Abu Marawat iron ore deposit, Eastern Desert of Egypt', Internal report, Geol. Surv. Egypt, 1969.

Bakker

R. J.

: ‘Package FLUIDS 1. Computer programs for analysis of fluid inclusion data and for modeling bulk fluid properties', Chem. Geol., 2003, 194, 3–23.

Basta

F. F.

, Takla

M. A.

and Maurice

A. E.

: ‘The Abu Marawat banded iron formation: geology, mineralogy, geochemistry and origin’, Proc. 5th Conf. on ‘The geology of the Arab World’, 319–334; 2000, Egypt, Cairo University.

Bennett

J. D.

and Mosley

P. N.

: ‘Tiered-tectonics and evolution, Eastern Desert and Sinai, Egypt’, in ‘Current research in african earth sciences' (ed. Matheis

and Schandelmeier

); 1987, Rotterdam, Balkema.

10.

Benning

L. G.

and Seward

T. M.

: ‘Hydrosulphide complexing of Au(I) in hydrothermal solutions from 150-400°C and 500-1500 bar', Geochim. Cosmochim. Acta, 1996, 60, 1849–1871.

11.

Bodnar

R. J.

: ‘Revised equation and table for determining the freezing point depression of H20—NaC1 solutions', Geochim. Cosmochim. Acta, 1993, 57, 683–684.

12.

Borg

, Lyatuu

D. R.

and Rammlmair

: ‘Genetic aspects of the Geita and Jubilee Reef Archaean BIF-hosted gold deposits, Tanzania', Geologische Rundschau, 1990, 79, (2), 355–371.

13.

Botros

N. S.

: ‘Geological and geochemical studies on some gold occurrences in the north Eastern Desert, Egypt', PhD thesis, Zagazig University, Zagazig, Egypt, 1991, 146.

14.

Botros

N. S.

: ‘New prospects for gold mineralisation in Egypt', Ann. Geol. Surv. Egypt, 1993, 19, 47–56.

15.

Brown

S. M.

, Johnson

C. A.

, Watling

R. J.

and Premo

W. R.

: ‘Constraints on the composition of ore fluids and implications for mineralising events at the Cleo gold deposit, Eastern Goldfields Province, Western Australia', Aust. J. Earth Set, 2003, 50, 19–38.

16.

Cathelineau

: ‘Cation site occupancy in chlorites and illites as a function of temperature', Clay Miner, 1988, 23, 471–485.

17.

Collins

P. L. F.

: ‘Gas hydrates in CO2-bearing fluid inclusions and the use of freezing data for estimation of salinity', Econ. Geol., 1979, 74, 1435–1444.

18.

Dardir

A. A.

and El Shimi

K. A.

: ‘Geology and geochemical exploration for gold in the Banded Iron Formation of Um Nar area, Central Eastern Desert, Egypt', Ann. Geol. Surv. Egypt, 1992, 18, 103–111.

19.

David

J. H.

: ‘Abu Marawat prospect, Central Eastern Desert of Egypt: a review and assessment of work carried out by Minex-Minerals, Egypt', Internal report, Geol. Surv. Egypt, 1988.

20.

Diamond

L. W.

: ‘Introduction to phase relations of CO2—H20 fluid inclusions’, in ‘Fluid inclusions in minerals: methods and applica-tions', (ed. de Vivo

and Frezzotti

M. L.

), 131–158; 1994, Blacksburg, Virginia Tech.

21.

EGSMA: ‘Geologic map of Al Qusayr Quadrangle, Egypt', Geol. Surv. Egypt, Cairo, 1992.

22.

Eldougdoug

: ‘Gold anomalies in the Late Proterozoic felsic-mafic volcano-sedimentary sequence and associated rocks, Gebel Abu Marawat area, Eastern Desert, Egypt', Bull. Fac. ScL, Cairo Univ., 1990, 58, 533–548.

23.

El Habaak

G. H.

and Soliman

M. F.

: ‘Rare earth element geochemistry of the Egyptian banded iron formations and the evolution of the Precambrian atmosphere and ocean’, Proc. 4th Conf. on ‘Geochemistry', vol. 2, 149–160; 1999, Alexandria, Alexandria University.

24.

El-Mezayen

A. M.

, Hassaan

M. M.

, El-Hadad

and Hassanein

M. M.

: ‘Petrography, geochemistry and ore microscopy of Abu Marawat metavolcanics and associated gold mineralisation, North Eastern Desert, Egypt', Bull. Fac. Set, Al-Azhar Univ., 1995, 6, (2), 1999–2021.

25.

El Ramly

M. F.

: ‘A new geological map for the basement rocks in the Eastern Desert and Southwestern Deserts of Egypt, scale 1:1000000', Ann. Geol. Surv. Egypt, 1972, 11, 1–18.

26.

El Ramly

M. F.

, Greiling

R. O.

, Kroner

and Rashwan

A. A.

: ‘On the tectonic evolution of the Wadi Hafafit area and environs, Eastern Desert Egypt', Fac. Earth ScL, University Jeddah, Bull., 1984, 6, 113–126.

27.

Essawy

M. A.

and Abu Zeid

K. M.

: ‘Atalla felsite intrusion and its neighbouring rhyolitic flows and tuffs, Eastern Desert, Egypt', Ann. Geol. Surv. Egypt, 1972, II, 271–281.

28.

Fowler

, Ali

K. G.

, Omar

S. M.

and Eliwa

H. A.

: ‘The significance of gneissic rocks and synmagmatic extensional ductile shear zones of the Barud area for the tectonics of the North Eastern Desert, Egypt', J. Afr. Earth Set, 2006, 46, 201–220.

29.

Fritz

, Wallbrecher

, Khudeir

A. A.

, Abu El-Ela

and Dallmeyer

D. R.

: ‘Formation of Neoproterozoic metamorphic core complexes during oblique convergence (Eastern Desert, Egypt)', J. Afr. Earth Set, 1996, 23, 311–329.

30.

Garson

M. S.

and Krs

: ‘Geophysical and geological evidence of the relationship of Red Sea transverse tectonics to ancient features', Bull. Geol. Soc. Am., 1976, 87, 169— 181.

31.

Greiling

R. O.

, Kröner

, El-Ramly

M. F.

and Rashwan

A. A.

: ‘Structural relationships between the southern and central parts of the Eastern Desert of Egypt: details of a fold and thrust belt’, in ‘The Pan-African Belt of Northeast Africa and adjacent areas', (ed. El-Gaby

and Greiling

R. O.

), 121–146; 1988, Weisbaden, Vieweg & Sohn.

32.

Gross

G. A.

: ‘Tectonic systems and the deposition of iron formations', Precamb. Res., 1983, 20, 171–187.

33.

Habib

M. E.

: ‘Arc ophiolites in the Pan-African basement between Meatiq and Abu Furad, Eastern Desert, Egypt', Bull. Fac. Sci., Assiut Univ., 1987, 241–283.

34.

Habib

M. E.

, El-Gaby

and El-Nady

O. M.

: ‘Structures and deformational history of the area west of Gabal El-Rubshi, Eastern Desert, Egypt', Bull. Fac. Set Assiut Univ., 1978, 7, 99–114.

35.

Hagemann

S. G.

and Cassidy

K. F.

: ‘Archaean orogenic lode gold deposits', Rev. Eco. Geol., 2000, 13, 9–68.

36.

Hilmy

M. E.

and Osman

: ‘Remobilization of gold from a chalcopyrite—pyrite mineralisation Hamash gold mine, Southeastern Desert, Egypt', Miner. Depos., 1989, 24, 244–249.

37.

James

H. L.

: ‘Sedimentary facies of iron formation', Econ. Geol., 1954, 49, 235–293.

38.

Konhauser

K. O.

, Hamade

, Raiswell

, Morris

R. C.

, Ferris

F. G.

, Southam

and Canfield

D. E.

: ‘Could bacteria have formed the Precambrian banded iron formations?', Geology, 2002, 30, 1079–1082.

39.

Kranidiotis

and MacLean

W. H.

: ‘Systematics of chlorite alteration at the Phelps Dodge massive sulphide deposit, Matagami, Quebec', Econ Geol., 1987, 82, 1898–1991.

40.

Mikucki

: ‘Hydrothermal transport and depositional processes in Archaean lode—gold systems: a review', Ore Geol. Rev., 1998, 13, 307–321.

41.

Mumin

A. H.

, Fleet

M. E.

and Chryssoulis

S. L.

: ‘Gold mineralisation in As-rich gold ores of the Bogosu-Prestea mining district of the Ashanti gold belt, Ghana: remobilization of the “invisible gold”, Miner. Depos., 1994, 29, 445–460.

42.

Pal

and Mishra

: ‘Alteration geochemistry and fluid inclusion characteristics of the greenstone-hosted gold deposit of Hutti, Eastern Dharwar Craton, India', Miner. Depos., 2002, 37, 722–736.

43.

Phillips

G. N.

and Powell

: ‘Link between gold provinces', Eco. Geo., 1993, 88, 1084–1098.

44.

Ramboz

, Pichavant

and Weisbrod

: ‘Fluid immiscibility in natural processes: use and misuse of fluid inclusion data. II. Interpretation of fluid inclusion data in terms of immiscibility', Chem. Geol., 1982, 37, 29–48.

45.

Ries

A. C.

, Shackelton

R. M.

, Graham

R. H.

and Fitches

W. R.

: ‘Pan-African structures, ophiolites and melange in the Eastern Desert of Egypt: a traverse at 26°N', J. Geol. Soc., London, 1983, 140, 75–95.

46.

Sabet

A. M.

and Bondonosov

V. P.

: ‘The gold ore formations in the Eastern Desert of Egypt', Ann. Geol. Surv. Egypt, 1984, 14, 35–42.

47.

Sabet

A. H.

, Shmelov

and Bordonosov

V. P.

: ‘Results of prospecting for gold and rare metals in Wadi Safaga El Barrud, El Marah and Hamama', Internal Report, Geol. Surv. Egypt, 1977.

48.

Saha

and Venkatesh

A. S.

: ‘Invisible gold within sulphides from the Archaean Hutti-Maski schist belt, Southern India', J Asian Earth Set, 2002, 20, 449–457.

49.

Shepherd

T. J.

, Rankin

A. M.

and Alderton

D. H. M.

: ‘A practical guide to fluid inclusion studies', 1985, London, Blackie.

50.

Sibson

R. H.

: ‘Seismogenic framework for hydrothermal transport and ore deposition', Soc. Econ. Geol. Rev., 2001, 14, 25–50.

51.

Sibson

R. H.

, Robert

and Poulsen

K. H.

: ‘High angle reverse faults, fluid pressure cycling and mesothermal gold deposits', Geology, 1988, 16, 551–555.

52.

Sims

P. K.

and James

H. L.

: ‘Banded iron formation of later proterozoic age in the Central Eastern Desert, Egypt: geology and tectonic setting'. Econ. Geol., 1984, 79, 1777–1784.

53.

Stern

R. J.

: ‘Petrogenesis and tectonic setting of Late Precambrian ensimatic volcanic rocks, Central Eastern Desert of Egypt', Precamb. Res., 1981, 16, 195–230.

54.

Sturchio

N. C.

, Sultan

and Batiza

: ‘Geology and origin of Meatiq dome, Egypt: a Precambrian metamorphic core complex?' Geology, 1983, 11, 72–76.

55.

Unzog

and Kurz

: ‘Progressive development of lattice preferred orientations (LP0s) of naturally deformed quartz within a transpressional collision zone (Panafrican Orogen in the Eastern Desert of Egypt)', J. Struct. Geol., 2000, 22, 1827–1835.

56.

Van Straaten

H. R.

: ‘Gold mineralisation in Tanzania: a review’, in ‘The geology, geochemistry and genesis of Gold Deposits, Gold ‘82', (ed. Foster

R. R.

), Spec. Publ. Geol. Soc. Zimbabwe, 1984, 11, 673–685.

57.

Zaki

M. E.

, Botros

N. S.

, Zakhari

, and Abdel Tawab

M. M.

: ‘Geochemical exploration of Abu Marawat and Fatiri gold ore deposit', Internal report, Geol. Surv. Egypt, 1987.

58.

Zhang

Y. G.

and Frantz

J. D.

: ‘Determination of the homogenisa-tion temperatures and densities of supercritical fluids in the system NaC1—KC1—CaC12—H20 using synthetic fluid inclusions', Chem. Geol., 1987, 64, 335–350.

59.

Zoheir

B. A.

: ‘Gold mineralisation in the Um El Tuyor area, South Eastern Desert, Egypt: geologic context, characteristics and genesis', PhD thesis, Ludwig-Maximilians Universität (LMU) München, Germany, 2004, 159.

60.

Zoheir

B. A.

, Akawy

and Hassan

: ‘Role of fluid mixing and wallrock sulfidation in gold mineralisation at the Semna mine area, central Eastern Desert of Egypt: evidence from hydrothermal alteration, fluid inclusions and stable isotope data', Ore Geol. Rev., 2008, 34, (4), 580–596.