Application of Area Selection Criteria (ASC) For Exploration of Economically-Viable Volcanic Massive Sulphide (VMS) Deposits at Wetar Island, South West Maluku – Indonesia PDF

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PROCEEDINGS Joint Convention Balikpapan 2015 HAGI-IAGI-IAFMI-IATMI 5–8 October 2015 Application of Area Selection Criteria (ASC) For Exploration of Economically-Viable Volcanic Massive Sulphide (VMS) Deposits at Wetar Island, South West Maluku – Indonesia Omar Syarief1, Ambang Wisbagyono1, Chris Far...

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T went y five more years of mineral explorat ion and discovery in Indonesia (1993-2017) T heo M van Leeuwen T he development of volcanic host ed massive sulfide and barit e–gold orebodies on Wet ar Island, Indo… Richard J Herringt on Mineral Deposit s of Sulawesi T heo M van Leeuwen

PROCEEDINGS Joint Convention Balikpapan 2015 HAGI-IAGI-IAFMI-IATMI 5–8 October 2015

Application of Area Selection Criteria (ASC) For Exploration of Economically-Viable Volcanic Massive Sulphide (VMS) Deposits at Wetar Island, South West Maluku – Indonesia Omar Syarief1, Ambang Wisbagyono1, Chris Farmer2, 1. PT. Batutua Kharisma Permai; Patra Jasa Office Tower 9th Floor, Jl. Jend. Gatot Subroto Kav 32-34 Jakarta 12950 Indonesia, 2. Finders Resources Ltd; Suite 901, Level 9, 60 Pitt Street, Sydney, NSW, Australia Abstract A desktop study and geological analysis on current Wetar Project datasets were carried out to establish certain key criteria which related to the volcanic massive sulphide mineralization processes and the deposition of economic resources in the Wetar mineralization district. The primary objective is to identify deposit-scale exploration targets with potential to be developed into mineable copper and/or gold reserves within Batutua’s tenements at Wetar Island.

objectives. Conceptually objectives are to organize data for enhancing geological understanding and establish geological model for similar deposit type within similar prospective environment, and in Wetar Exploration case, the ASC practically will be utilized for decode the mystery of VMS cluster at Wetar island and as guidance for localscale and deposit-scale targeting. Mineral exploration project principally involves a number of interlinked and sequential programs to reduce risks and although in the contrary increase expenditures (Fig. 1).

The first stage of the study is the identification of regional tectonic scale structures that may concentrate the flow of fluids (magma and metal-bearing fluids). The intersection of structural zones, characterized by inverted rifts, defines the prospective mineralization belts and determines campscale and deposit-scale targets. Camp-scale and deposit-scale targeting involves analyses and interpretation of more detailed geological and structural datasets, together with geophysical and mineral occurrence data to define specific areas of exploration potential. All targets are ranked on a technical basis utilizing ASC criteria and a simple numerical scoring scheme. Key criteria comprise favorable geological setting including specific host rocks, uplift and erosion rates, prospect scale faulting, post-mineral cover and mineral occurrences or alteration assemblages. Keyword: Area Selection Criteria (ASC), Wetar mineralization district, volcanic massive sulphide (VMS), camp-scale target, deposit-scale target

Early stages of exploration project comprise of planning and reconnaissance phases which mainly purposed for break-down larger regional-scale district into local-scale area for detail ground work. The processes vary depend on; the selection of commodity, type of deposit, exploration methods, and the setting up of an exploration organization. Figure 1: Stages of an exploration project (Eimon 1988).

Introduction Area Selection Criteria (ASC) can be defined as series of criteria based on presence or absence of specific geological features, or alternatively geophysical and geochemical features. Due to its function as evaluation tool, ASC also being defined as measurable descriptive features of several representatives conceptual model type and or empirical standard which embody the essential features of some population of natural geological phenomena (Hodgson, 1990). Some objectives were attributed to this ASC, and can be categorized into conceptual objectives and practical

Particularly for exploration of hydrothermal-related mineralization, area break-down is defined and being simplified by relation between mass concentrative system of chemical process in hydrothermal fluids and favorable geological settings especially structural control (Fig.2). Regional scale is being defined as broad area/region where the primary hydrothermal fluid being sourced, usually situated in actively deforming basement structure. Hydrothermal fluid being transported in many varieties of pathways and accumulated to form fluid reservoir, in some ways these reservoirs may trap by fluid flow-barrier in

PROCEEDINGS Joint Convention Balikpapan 2015 HAGI-IAGI-IAFMI-IATMI 5–8 October 2015 smaller zone named as camp-scale area. Fluid flow barriers have capability of trapping fluid and pressure necessary for later emplacement/sedimentation of economic minerals in small concentrated discharge area in/or near surface which defined as deposit-scale area.

geological criteria. Target score summaries are presented in Table 1. Criteria Strong and Continuous VMS Mineralization (C1)

This ASC assignment were utilizing some datasets; mainly originated from Batutua/Finders’s data, some levels of historical PLM (Billiton) data, related government institutions, and other relevant data from unclassified sources. Primary Batutua dataset mostly already in digital format, while other complementary datasets have to be translated into Batutua definition before converted into acceptable digital data.

Generic

Data and Method

Early stage of framework analyses involved identification, synthesis and interpretation of regional tectonic scale structures that may concentrate the flow of fluids (magma and metal-bearing fluids), establishing representative geological model for VMS at the same mineralization district, and generate key geological criteria leading to formation of VMS deposits in the area.

Strong and Continuous VMS Alteration (C3)

Proximity to Paleosurface (C4)

Specific

The analysis then followed by camp-scale target development which involved more detailed geological information and structural datasets, together with geophysical and mineral occurrence data to define critical process element for mineralization to be occurred. Finally, the deposit-scale target being defined by more detailed possible-relevant geological and geophysical manifestations.

Favorable Structural Site (C2)

Favorable Associated Volcanic Rocks (C5)

Key Manifestations

 Presence of massive sulphide and/or sulphide stockwork mineralization, continuity of massive sulphide generally parallel to stratigraphy  Geophysical response consistent with massive sulphide and/or sulphide stockwork, some combination of EM, IP, gravity, and Magnetic signatures  High Cu anomaly and/or indication of increase in grade towards the core of a VMS system.  Structural context indicative of likely continuity of mineralization along strike and down plunge  Indication of syn-volcanic structure (stratigraphic offset in footwall only, dykes, debris flows)  Minimal post mineral deformation in the ore environment

 Intense chloritic and possibly silicification in the footwall of the massive sulphide  Intense sericitic alteration showing a lateral vector towards ore zone (geochemical or mineralogical)  Area with Na2O-CaO depletion and MgOK2O enrichment  Alteration focused in the stratigraphic footwall  Presence of exhalite which can consist of baritic sand, Fe-chert, jasper, cherty tuff, tuffaceous exhalite  Anomalous geochemistry within the exhalite, including base metals and gold, providing vector towards ore zone  Debris flows with exhalite clasts and massive sulphide clasts  Volcanic rocks, most commonly at the margin of domes and small volume flows and pyroclastic rocks.  Dacitic, andesitic, or basalt (confirmed by geochemistry), most favorable is the upper part of the volcanic sequence (not necessarily the very top).

Weight 35

25

15

15

10

Each criterion is assigned a score between 0 and the maximum score (weigh score), score 0 if criteria not occurs/absent and the maximum score for area with highly favorable (with respect) to the criterion. Two type of scoring were applied to each area; (1) potential value is possible score on how favorable the area on involved criterion, and (2) confidence score which depend on the quality and quantity of the involved criterion. Final total potential and confidence scores are simple sums of those scores for individual criteria. Figure 2: Mineral system framework; (a) Ore genesis as the focus of a scale-hierarchical mass concentrative system (McCuaigh and Hronsky 2013), (b) Schematic summary of the camp concept. A numerical target ranking methodology, based on critical targeting elements for VMS deposit where geological and or geophysical criteria could be identified from available datasets with certain weighing factors for specific

Table 1: Table for evaluating Deposit-Scale target Application for Wetar Copper Project The study on regional-scale tectonic has summarized that Wetar Island is located on the Inner Banda Arc in Eastern Indonesia. It is part of a chain of volcanic islands caused by the collision of the Australian plate moving beneath the SE Asia plate (Fig 3). Wetar Island itself situated in

PROCEEDINGS Joint Convention Balikpapan 2015 HAGI-IAGI-IAFMI-IATMI 5–8 October 2015 extensional tectonic regime of back arc setting, responsible for the rising of highly volatile magmas which associated with atypical gold-rich VMS deposits seen on Wetar.

Matagami district of Japan to over 100 Mt (19 deposits) at Noranda district in Canada.

Figure 3: Simplified Cross-Section of the Banda Orogen (Scotney et al 2005) The geology of Wetar broadly comprises of MiocenePliocene volcanic sequences ranges from basaltic to dacitic composition, locally intercalated with Pliocene deep marine sediments which include a globigerina limestone unit and a Quaternary package of dacitic volcanics and andesitic epiclastics and volcanoclastics. Economic minerals were observed along/or near contact between volcanic sequence as copper-rich VMS and goldsilver stratiform barite sand, clay or silt above massive pyritic sulphide mounds (Sewell and Weatley, 1994).  Camp-scale hydrothermal alteration observed over 25 km2 around Kali Kuning and Lerokis. The most intense alteration assemblage is clay-chlorite with disseminated pyrite (and rarely sphalerite/chalcopyrite). Clay minerals comprise of kaolinite-illite (occur mostly near surface), and montmorillonite or sericitic clay observed in the fault zones. Silicifications occur intensely in the vicinity of known deposits, partially exhibit epithermal-like textures. In bigger scale, regional-scale limonitic anomalous zones were delineated from Landsat (and other satellite images).

The Wetar district has an extraordinary amount of metal occurrences, tens of surface copper and gold occurrences were observed by historical explorer, although only small numbers were ever developed Figure 4: Comparison of Wetar and the VMS district in Canada and Japan (modified after Sangster, 1980) Batutua (subsidiary of Finders Resources) currently developed and defined a numbers of potential targets at different level of exploration and development stages (Fig 5), current ASC is being employed in some decision points to make recommendation for moving up targets into higher stages or out of the exploration pipeline.

For the purpose of defining whether Wetar Island is favorable and fertile for evaluated deposit types, a comparison has been made between Wetar Mineralization District to relatively well-known VMS districts in Canada and Japan where typically massive sulphide occur in cluster at specific stratigraphic horizon. Wetar VMS mineralization district also convincingly exhibit cluster mineralization occurrences. Although the number of deposits and combined resources known on Wetar are very small compared to other VMS district (Fig 4). The three known deposits at Wetar VMS district account for approximately near 10 Mt of ore. The number of deposits and size of VMS in Canada and Japan is significantly larger ranging from 34 Mt (10 deposits) in

Figure 5: Wetar copper project exploration and development pipelines

PROCEEDINGS Joint Convention Balikpapan 2015 HAGI-IAGI-IAFMI-IATMI 5–8 October 2015 Some of these potential targets already been drilled and being confirmed of having VMS-type mineralization. In addition, a number of new targets also being defined by Batutua as result of its recent program, respectively; KK East and KK West, Baru Manu East, and Karkopang. This paper provide detail synthesis of selected deposit with regard of observed criteria for VMS association, Meron prospect was selected as representation of most advance target since its current resources development status, and due to availability of exploration datasets (Table 2): Target Name Meron Current Stage Resource Development ASC Summary and Score C1

C2

C3

C4

C5

 Numerous historical drillholes intersected VMS at various depth and thickness, VMS dipping toward N and NW directions  Excellent EM anomaly signatures  Associated with gold-bearing sedimentary exhalative overlies the VMS body  Situated along same mineralization structure with Kali Kuning deposit  Minor post-genetic fault which could displaced the mineralization body  Broad VMS-like alteration were observed  Strong limonitic-jarositic surface overprinting broadly replaced original sulphide minerals  Gossanous exhalative unit (baritic sand) was observed over the outcropped VMS body  Chert/cherty jasper? observed in some places  Composed of similar volcanic rocks suits as Kali Kuning deposit.  Mineralization observed along contact between andesiticdacitic footwall with dacitic hangingwall

Total Score

33

C4

C5

Total Score

Table 3: Prospect

C1

C2

C3

C4

C5

Total Score

Rank

33 34 25 15 18 19 20 20

21 18 21 15 17 21 15 15

12 14 8 10 12 8 10 12

13 14 5 5 8 5 10 13

6 8 6 4 5 6 10 6

85 88 65 43 60 59 65 66

1 1 2 3 2 3 2 2

13

* Total score >80 = rank 1, total score 80-60 = rank 2, total score...