Structural Development and Mineralization of the Western Edmund and Collier Basins

Structural development and mineralization of the western Edmund and Collier Basins

by AM Thorne, SP Johnson, HN Cutten, and O Blay

Low-grade metasedimentary rocks of the Paleoproterozoic the north of the Talga Fault, the maximum thickness of to Mesoproterozoic Edmund and Collier Basins form Depostional Packages 1 and 2, in the lower part of the the youngest depositional elements within the Capricorn Edmund Group (Fig. 1), is ~1.5 km, whereas to the south Orogen (Fig. 1). The succession comprises ~4 to 10 km of they increase to ~3.75 km thick. Across the Godfrey Fault, mainly fine-grained siliciclastic and carbonate sedimentary Depositional Packages 1 and 2 increase in thickness from rocks that were deposited in a variety of shelf to basinal ~6 km to ~8.25 km. Depositional Packages 1 and 2 are environments (Martin and Thorne, 2004). Sediments in also consistently thicker in the hangingwall of the basin- the Edmund Basin were deposited unconformably on bounding extensional faults, suggesting that extensional Paleoproterozoic basement rocks, including the Gascoyne downthrow on these major faults was toward the Province, sometime between c. 1620 and c. 1465 Ma, southwest. Depositional Package 2 is not present south of based on the ages of the underlying Gascoyne Province a line joining the Geegin Syncline with the Mount Vernon and intrusive Narimbunna Dolerite. Sediments in the Fault, presumably having been incised and eroded away unconformably overlying Collier Basin were deposited prior to the deposition of Depositional Package 3, which across both the Paleoproterozoic basement and locally is up to 3 km thick in this area. deformed sedimentary rocks of the Edmund Basin, after the Mutherbukin Tectonic Event at c. 1200 and before intrusion of the c. 1070 Ma Kulkatharra Dolerite. Collier Basin Deposition in the Collier Basin (Depositional Packages Edmund Basin 5 and 6 of the Collier Group) appears to have been less influenced by synsedimentary fault movements The Edmund Basin corresponds to the present day (Martin and Thorne, 2004), although the principal basin outcrop of the Edmund Group. It contains four architecture parallels the main northwest–southeast to sedimentary packages whose depositional character was east–west structural trends seen within the underlying ultimately controlled by the primary orientation and Edmund Basin and Gascoyne Province. repeated reactivation of major crustal structures in the Paleoproterozoic basement. These include the Talga, Godfrey, and Lyons River Faults in the west, and the Quartzite Well, Bujundunna, and Mount Vernon Faults in Mutherbukin Tectonic Event the east. Recently acquired deep seismic reflection data (1385–1200 Ma) (Johnson et al., 2011a; Korsch et al., 2011) has highlighted the importance of the Talga, Godfrey, and Lyons River A major period of basin inversion took place during the Faults, which are imaged as mantle-linked structures that 1385–1200 Ma Mutherbukin Tectonic Event (Johnson dip steeply at the surface but become gently southward- et al., 2011b), prior to deposition in the Collier Basin. dipping in mid- to lower-crustal levels. The Lyons River In the underlying Gascoyne Province, this event was Fault has further significance in that it marks the early responsible for localized medium-grade metamorphism Paleoproterozoic crustal suture between the Glenburgh and deformation; however, evidence from the Edmund Terrane of the Gascoyne Province, and the Bandee Seismic Basin has been more difficult to interpret, due to the very Province of the Pilbara Craton. low grade nature of the metamorphism and difficulty in separating Mutherbukin-aged structures from similar, often Following the termination of the Mangaroon Orogeny at coaxial, features formed during the later 1030– 955 Ma c. 1620 Ma, extensional reactivation took place on the Edmundian Orogeny. Talga, Godfrey, Lyons River, Quartzite Well, Bunjindunna, and Mount Vernon Faults. Siliciclastic and carbonate Faults such as the Deverell Fault, in the eastern part of the sediments were deposited in the resulting half grabens, Edmund Basin, have large, sinistral, strike-slip offsets, which show significant sediment thickness variations but show only small offsets in the overlying Collier Basin, across the main structures. On the Pingandy Shelf to suggesting pre-Edmundian Orogeny movements. These

20 GSWA extended abstracts 2012 — Promoting the prospectivity of Western Australia

Lyons Group Edmund Group (Edmund Basin) Diamictite, sandstone and siltstone (locally Discovery, Devil Creek, Ullawarra, and Coodardoo calcareous), shale, and boulder beds and lags Formations (Package 4) Unassigned units Kiangi Creek, and Muntharra Formations (Package 3) Gooragoora, Blue Billy, and Cheyne Springs Formations (Package 2) Dolerite dykes, sills, or plugs Yilgatherra, and Irregully Formations (Package 1) Quartz vein or pod; Mount Augustus Sandstone c. 570 Ma Mulka Tectonic Event Mundine Well Dolerite Suite 1680–1620 Ma Mangaroon Orogeny Unassigned units 1030–955 Ma Edmundian Orogeny Massive metadolerite and foliated amphibolite Thirty Three Supersuite (Gascoyne Province) Metadolerite Leucocratic granite and metagranite, and pegmatite Durlacher Supersuite Granite and minor gabbro and Gifford Creek Carbonatite Complex metamorphosed equivalents Ferroan carbonatite; sills and dykes of Fe- carbonate Pooranoo Metamorphics Hematite–magnetite veins Pelitic and psammitic schist, quartz metasandstone, feldspathic metasandstone Kulkatharra Dolerite and metaconglomerate, and phyllite Collier Group (Collier Basin) Mount James Subgroup Ilgarari Formation (Package 6) 1820–1770 Ma Capricorn Orogeny 22°15' Backdoor Formation and Calyie Formation Moorarie Supersuite (Package 5) Undivided; granite and minor gabbro Cu,Au,Ag, 1385–1200 Ma Mutherbukin Tectonic Event

115°30' Pb,Zn,Mn Gooche Gneiss Narimbunna Dolerite Massive, subophitic metagabbro Cu Mount Leake Spring Metamorphics Murray Pelitic and psammitic schist

W Nanutarra Pb,Cu,U,Zn,Ag 2005–1950 Ma Glenburgh Orogeny

Pb Province Gascoyne Fe,Mag Marb Unassigned units Mt Alexander Mager Well W Pb,Ag,Cu Cu,Au Kilba W ell Pb Amphibolite Pb,Ag Plagioclase–actinolite–tremolite gneiss Thowagee Glen Florrie Pb Pb,Ag Cu,Au Fine- to medium-grained ultramafic schist Pb,Ag Pb Camel Hills Metamorphics Pb,Ag Telfer River Pelite, calc-silicate rock Th Kooline Pb Mundong Well Pb,Ag Dalgaringa Supersuite Qtza U,Cu Pb Pb,Ag Qtza Metagranite and granitic gneiss Mt Mortimer Moogie Metamorphics Cu,Pb Pingandy U Psammitic and pelitic schist Au,Ag,Pb Halfway Gneiss Cu,Pb,Ag Cu Bali Hi Interlayered leucocratic and mesocratic granitic Pb,Au,Zn,Ag 4000 gneiss Ullawarra Cu Dmd Pb,Cu 10GA–CP2 Marb,Dst 5000 Godfrey Fault Soldiers Secret

6000 Study Area Wanna SynclineShelf Top Camp Au,Ag,Cu,Pb Cu Au,Cu 7000 Au,Ag YangibanaREE Star of Mangaroon Talga Fault REE Frasers Lyons8000 River Fault 24°00' Mn Zn Nina Zn W,Mo,Au Geegin Syncline

McCarthys Patch Mn 118°45' 9000 Cobra Minnie Springs Mo,Au,Cu Mn Eldorado 10000 Mount Vernon Fault Mn Mn

Mo,Cu Bi

Nardoo W Qtza Tur 11000 Qtza Brl,Nb,Ta Bi Yinnietharra Bujundunna Brl,Ta,Nb Duncan Pool Ta,Nb,Brl,Tur Ta Brle Ta,Nb Reid Well W,Sn Fault Bi Quartzite Well Fault Au,Pb,Cu,Ba Manganese Range 12000 Pb,Au Pb,Cu,Zn,Au,Ba Abra Brl,U U U U Mn Brl Deverell Fault 13000 Mulgul Cu U Minindi Creek Discovery Gossan U Cu,Zn 9000 West Point Seismic line, W

with CDP points Hibernian Fault, major 25°00' Fault, minor Anticline Syncline 50 km Mineralization site AMT194 19.01.12

Figure 1. Geological map of the western Capricorn Orogen, showing the location of the principal structural elements within the Edmund and Collier Basins. The location of the deep seismic transect 10GA–CP2 is also shown.

21 Structural development and mineralization of the western Edmund and Collier Basins Thorne et al.

features are replicated in the Wanna Syncline, where the related to the c. 570 Mulka Tectonic Event. The main D1ed intensity of faulting is signiﬁcantly greater in the Edmund event resulted from northeast–southwest transpression,

Basin than in the Collier Basin. Although Mutherbukin and whereas the later D2ed event was caused by weak east- Edmundian structures are generally coaxial, an exception southeast to west-northwest compression. It is currently occurs in the western Wanna Syncline, where rocks of the unclear how the D1ed and D2ed folding and faulting events Edmund Group’s Depositional Package 1 record localized, in the Edmund and Collier Basins relate to localized north-northwesterly vergent reverse faulting and associated amphibolite-grade metamorphism, deformation, and granite folding of the Mutherbukin Tectonic Event, which has been intrusion in basement rocks of the Gascoyne Province refolded during later, northeasterly directed compression (Sheppard et al., 2007). during the Edmundian Orogeny. In the western and central Edmund and Collier Basins, Due to the brittle nature of faulting in the Edmund the fold and fault structures trend west–east to northwest– Group, direct age constraints on fault movements are southeast, and are concordant with both the general rare. However, authigenic illite from a fault gouge that basin architecture and the regional-scale structures in the displaces sandstone and siltstone beds of the Kiangi Creek underlying Gascoyne Province basement. Faults are steep, Formation (Fig. 2) has been dated at 1171 ± 25 Ma using and often occur as zones of quartz veining or brecciated the 40K/40Ar method (GSWA, unpublished data), which is quartz in an ironstone matrix. Folds are generally upright close to the younger age limit of the Mutherbukin Tectonic and open, but are tightened adjacent to faults, and Event. generally plunge gently to the northwest or southeast.

Edmundian Orogeny (1030–955 Ma) Mulka Tectonic Event (c. 570 Ma) The 1030–955 Ma Edmundian Orogeny was responsible for The c. 570 Ma Mulka Tectonic Event is responsible for low to very low grade metamorphism and transpressional late-stage, dextral, brittle–ductile faults and shears, with folding in the Edmund and Collier Basins. Martin et al. associated quartz veins, in rocks of the Edmund and

(2005) identiﬁed three distinct deformation events (D1ed, Collier Basins and Gascoyne Province. The faults also D2ed, and D3ed), although D3ed is now considered to be cut and offset dolerite dykes belonging to the c. 755 Ma Mundine Well Dolerite Suite (Sheppard et al., 2010).

Mineralization The Edmund and Collier Basins have a history of minor gold, base metal, and phosphate production; however, a major orebody, the Abra polymetallic deposit, has also been discovered in these rocks. This deposit occurs in a fault-bounded structural corridor that links up with the mantle-tapping Lyons River Fault system, together with other prospective deposits, including vein-hosted gold mineralization at Cobra, and vein-hosted copper mineralization in Collier Group rocks at Ilgarari and Kumarina. The formation of giant orebodies is often linked to the presence of crustal-scale plumbing systems that concentrate fluids, energy, and metals into specific sites in the crust. Many of these plumbing systems are intimately related to fossil subduction zones or old AMT193 18 01 12 cratonic margins. The depositional and deformational history of the Edmund and Collier Basins was controlled by pre-existing crustal-scale structures in the underlying Figure 2. A small-scale reverse fault (~50 cm displacement) basement. These structures have also exercised a strong and associated folding in siltstone and thin-bedded sandstone of the Kiangi Creek Formation. 40K/40Ar control on mineralization, with the multiply reactivated geochronology on the fault gouge indicates that Paleoproterozoic fossil suture zone along the Lyons River the structure formed during the latter stages of the Fault, in particular, appearing to have played a key role in Mutherbukin Tectonic Event. orebody development (Tyler et al., 2011).

22 GSWA extended abstracts 2012 — Promoting the prospectivity of Western Australia

References Martin, DM and Thorne, AM 2004, Tectonic setting and basin evolution of the Bangemall Supergroup in the northwestern Capricorn Orogen: Johnson, SP, Cutten, HN, Tyler, IM, Korsch, RJ, Thorne, AM, Blay, O, Precambrian Research, v. 128, p. 385–409. Kennett, BLN, Blewett, RS, Joly, A, Dentith, MC, Aitken, ARA, Martin, DM, Sheppard, S and Thorne, AM 2005, Geology of the Goodwin, J, Salmon, M, Reading, A, Boren, G, Ross, J, Costelloe, RD Maroonah, Ullawarra, Capricorn, Mangaroon, Edmund, and Elliott and Fomin, T 2011a, Preliminary interpretation of deep seismic reﬂection Creek 1:100 000 sheets: Geological Survey of Western Australia, lines 10GA–CP2 and 10GA–CP3: crustal architecture of the Gascoyne 1:100 000 Geological Series Explanatory Notes, 65p. Province, and Edmund and Collier Basins, in Capricorn Orogen seismic and magnetotelluric (MT) workshop 2011: extended abstracts Sheppard, S, Johnson, SP, Wingate, MTD, Kirkland, CL and Pirajno, (preliminary edition) edited by SP Johnson, AM Thorne, and IM Tyler: F 2010, Explanatory Notes for the Gascoyne Province: Geological Geological Survey of Western Australia, Record 2011/25, p. 49–60. Survey of Western Australia, Perth, Western Australia, 336p. Johnson, SP, Sheppard, S, Thorne, AM, Rasmussen, B, Fletcher, IR, Sheppard, S, Rasmussen, B, Muhling, JR, Farrell, TR and Fletcher, Wingate, MTD and Cutten, HN 2011b, The role of the 1280–1250 IR 2007, Grenvillian-aged orogenesis in the Palaeoproterozoic Ma Mutherbukin Tectonic Event in shaping the crustal architecture Gascoyne Complex, Western Australia: 1030–950 Ma reworking of and mineralization history of the Capricorn Orogen, in GSWA 2011 the Proterozoic Capricorn Orogen: Journal of Metamorphic Geology, extended abstracts: promoting the prospectivity of Western Australia: v. 25, p. 477–494. Geological Survey of Western Australia, Record 2011/2, p. 1–3. Tyler, IM, Johnson, SP, Thorne, AM and Cutten, HN 2011, Implications Korsch, RJ, Johnson, SP, Tyler, IM, Thorne, AM, Blewett, RS, Cutten, HN, of the Capricorn deep seismic survey for mineral systems, in Joly, A, Dentith, MC, Aitken, ARA, Goodwin, J and Kennett, BLN Capricorn Orogen seismic and magnetotelluric (MT) workshop 2011, Geodynamic implications of the Capricorn deep seismic survey: 2011: extended abstracts (preliminary edition) edited by SP Johnson, from the Pilbara Craton to the Yilgarn Craton, in Capricorn Orogen AM Thorne, and IM Tyler: Geological Survey of Western Australia, seismic and magnetotelluric (MT) workshop 2011: extended abstracts Record 2011/25, p. 109–114. (preliminary edition) edited by SP Johnson, AM Thorne, and IM Tyler: Geological Survey of Western Australia, Record 2011/25, p. 101–108.