Significant evidence for the blind copper deposit in Wai Wajo

SIGNIFICANT EVIDENCE FOR THE BLIND COPPER DEPOSIT IN WAI WAJO AREA SIKKA DISTRICT, EAST NUSA TENGGARA PROVINCE,
REPUBLIC OF INDONESIA

By
Franklin Rajagukguk, Bambang Pardiarto, Bambang Setiawan
Directorate of Mineral Resources Inventory

 ABSTRACT

The Lowo Deba prospect is located in Wai Wajo area, Sikka district, East Nusa Tenggara province, Republic of Indonesia. The Wai Wajo prospect was discovered as a result of a systematic exploration program by Directorate of Mineral Resources (DMR) since 1999-2000 and 2002, and than proceed on the year 2003 – 2004 by DMRI – KORES, focused on base metal and precious metal mineralization.The geology of the prospect area consists of Miocene volcanics of Kiro Formation and Tanahau Formation and intrusive of granodiorite and Quaternary volcanics. From the chemical analysis results of major elements of representative volcanics shows characteristic of toleiitic magma. The predominant system of lineaments in the prospect area tends to be NE-SW trend. This fault system appears to have a closed relationship with the mineralization in Lowo Deba prospect.Most of base metal mineralization were hosted by phyllic – argillic andesitc to dacitic tuff of Kiro Formation and Tanahau Formation and intrusive of granodiorite with the occurrences of structure control of epithermal type or massive sulfide type. Rock samples indicate the mineralization types are disseminated, fracture filling and quartz vein containing chalcopyrite, galena, sphalerite, covellite and pyrite. The best grade revealed from these rocks of 6,980 ppm Cu and 50 ppb Au, and from quartz vein of 4,868 ppm Cu and 57 ppb Au.Geochemical anomaly zones identify two combined anomaly i.e. Au-Cu-Zn-Mo and Ag-Pb-Zn. Those anomalies are concentrated in the phyllic and argillic andesitic tuff of Kiro Formation. This anomaly area also occupied by base metal and gold mineralization outcrops.Interesting IP anomalies are found in electrode separation index of n=5 and n=7 in line WA7 with chargeability value of 405.7 Msec and resistivity value of 37.7 Ohm-m. In general high chargeability and low resistivity anomalies are developed of direction from southwest to northeast of prospect area and these anomalies still open to the northeast. The high chargeability value lets to predict presenting of blind copper deposits. Some bore holes will be proposed for the next survey to confirm the present of blind ore deposit in the prospect area. 

1. INTRODUCTION

This paper is the first to describe and interpret in detail the geology, geochemical and geophysical within Lowo Deba prospect as indicate significant evidence for the blind copper deposit in Sikka district, East Nusa Tenggara Province, Republic of Indonesia. The study based on quantitative of rock and mineral characteristics as well as geologic mapping, petrography, mineragraphy, fluid inclusion, rock chemistry and geochemical data and geophysical data. No attempt is made at this stage of investigation to compare the Wai Wajo blind copper deposit to other mineral occurrences.

 

1.1 Location and Access

 The Lowo Deba prospect lies within the following coordinates (UTM) of 392700 – 393300 mE and 9043000 – 9042500 mN, located in the Wai Wajo area, Sikka district, East Nusa Tenggara Province, Republic of Indonesia(Fig. 1). Domestic airlines provide daily service to the provincial capital of Maumere, and travel from there to southwest Mego sub district by road takes 45 minutes.

 

Fig.1 Location of prospect area1.2 Background of the project area

Korea Resources Corporation (KORES) and Directorate General of Geology and Mineral Resources (DGGMR) under The Memorandum of Understanding between KORES and DGGMR signed on June 7^th 2002 in Jakarta, concerning a joint Mineral Resources Inventory and Exploration in Indonesia conducted an exploration of the precious and base metal potential in Sikka-Ende Area, East Nusa Tenggara Province.The First Phase of Joint Mineral Exploration in Project area was started in 2003. The first phase of joint mineral Exploration between KORES and DMRI was regional survey involving geological and geochemical investigations and in order to make out the potential metallic mineral resources in the survey area.The second Phase survey aims to follow-up of the first Phase exploration data and information of precious and base metal prospect by elucidating the geologic setting, the relationship between mineralization and geologic structure, and the mode of occurrences of mineral deposits through geological survey, geochemical and geophysical prospecting and than delineate of large-scale area.

 

1.3 Discovery of prospect area

The Lowo Deba prospect was discovered as a result of a systematic exploration program by Directorate of Mineral Resources (DMR) since 1999-2000 and 2002, and than proceed on the year 2003 – 2004 by DMRI – KORES, focused on base metal and precious metal mineralization. In 1999, as well as Wai Wajo, the exploration team identified mineral occurrences of disseminated copper sulphides in Tertiary volcanic, granitic intrusion and quartz vein. Associated reconnaissance stream sediment and float sampling this area has identified some anomalous copper including gold. The Float assay from Lowo Mego River revealed of 10 % Cu and 520 ppb Au. Follow-up work in year 2000, the geophysics team has identified the geomagnetic anomaly showing NW-SE, N-S, and NE-SW trending similar to the fault structures. The mineralization was controlled by NE-SW trending fault and the andesite – diorite intrusion filled along this structure. The IP anomaly indicates the mineralization zone of the Lowo Mego still open to the NNE in Wai Wajo tributaries (Lowo Deba).In 2002 Directorate of Mineral Resources Inventory (DMRI) conducted follow-up work focusing in Lowo Mego and its tributaries (Lowo Deba) by geochemical soil ridge and spurs with 100 m interval each point sampling and made of 50 m long of trenching with 1 m sampling interval in the middle part of Lowo Deba creek. The results of the survey has identified strong anomalous zones of Cu-Pb-Mn-Mo in phyllic – advanced argillic Tertiary volcanic tuff and from trench shows well mineralization silicified andesitic. Rock assay revealed 4,980 ppm Cu and 45 ppb Au.By these data and information, the surface extension of mineralization at Lowo Deba was programmed in 2003 – 2004 by alteration mapping, trenching, geochemical soil grid system and geophysical prospecting (Induced Polarization method). Hopely the investigation will let to discover of blind deposit in the prospect area.

 

2. EXPLORATION RESULTS2.1 Geology Survey

According to existing geological maps, the regional geology of the project area is composed mainly of Tertiary volcanic rock, sedimentary and intrusive body and Quaternary volcanic rock (Fig. 2). While from the surface mapping, the geology of the prospect area consists of Miocene volcanics of Kiro Formation and Tanahau Formation and intrusive of granodiorite and Quaternary volcanics (Fig.3). From the chemical analysis results of major elements of representative volcanics in the Wai Wajo area are belong to calc-alkaline and tholeitic series based on Na₂O + K₂O versus SiO₂ diagram as seen in Figure 4.The predominant system of lineaments has been interpreted and extracted in the whole survey area tends to be NNW- NNE trend. High-density occurrences of lineaments are found in eastern part of Wai Wajo. Field observation and plotting of joints (Fig.5) from the prospect area are interpretated as two major lateral slip fault systems showing NE-SW and N-S trend. The NE-SW fault systems is the most dominant in the Lowo Deba prospect area and the mineralization in this area appears to have a closed relationship with this fault systems.Most of base metal mineralization was hosted by phyllic – argillic andesitc to dacitic tuff of Kiro Formation and Tanahau Formation and intrusive of granodiorite with the occurrences of structure control of epithermal or massive sulfide type. In Lowo Deba the mineralization generally has been found within hydrothermal alteration as argillic and advanced argillic andesitic tuff of Kiro Formation throughout structure opening (Fig.6). Rock samples indicated the mineralization types are disseminated, fractures filling and quartz vein (Fig.7) containing chalcopyrite, galena, sphalerite, covellite and pyrite. The best grade revealed of 6,980 ppm Cu and 50 ppb Au. The occurrences of quartz veins in the survey area closely related to structural control such as normal fault, lateral fault and opening as dilation jogs affected by both faults. The quartz veins are generally hosted by silicified andesitic tuff, altered dacitic lapilli tuff and granodioritic and the best grade revealed of 4868 ppm Cu and 57 ppb Au.Ore microscopic study (Fig.8) from some veins shows not any significant mineralization, however from hand specimen observation indicates some secondary minerals after chalcopyrite such as covellit, malachite and chalcocite are present.Ore microscopic indicates the paragenesis of several samples can be described as follows:PyriteChalcopyriteCovelliteChalcositeIron oxideFluid inclusions studies were examined in four samples of white to gray milky quartz derived from several hydrothermal veins around and along the Lowo Deba creek. The result of these examinations and calculations are shown in Table 1.Two types of primary inclusions were recognized in the survey area and classified according to the phases presented at room temperature and their behavior on heating and freezing. Each type is described as follows.

 

Type I : It consists of a liquid dominantly and a vapor phase and show filling degree of 80 to 90 vol. %. Type I inclusions are 10 to 25μm in size and are found in isolated, randomly distributed occurrences and show rounded shape. These inclusions are homogenized to the liquid phase upon heating and contain daughter minerals.

Type II : It is vapor-rich inclusions and show filling degree of 60 to 80-vol % at room temperature. These inclusions occur as primary and show irregular shape. They are usually 5 to 30μm in size. These inclusions are homogenized to the vapor phase upon heating and do not contain daughter minerals. Homogenization temperatures of primary liquid-rich H₂O type fluid inclusions in ore stage white to milky quartz from the deposits range from 177° C to 326° C (Figure 9). The ranges of homogenization temperatures of primary fluid inclusions in quartz related to the ore mineralization are different. Liquid-rich H₂O type inclusions in white to milky quartz related to main ore mineralization homogenize at relatively lower temperatures between 177° C and 284° C than these in barren quartz. Salinities of liquid-rich H₂O type inclusion in ore stage quartz related to ore mineralization range from 3.7 to 12.4 equiv. wt. % NaCl (Figure 10). During the mineralization episodes, variations in temperature and composition of the hydrothermal fluids are recorded by fluid inclusions. The homogenization temperatures of primary inclusions in main stage minerals range from 320° C to 170° C. Fluid inclusion data indicate that fluid evolved from initial high temperature (near 320° C) to lower temperature (near 170° C). Therefore, it is probable that Au and base metal mineralization occurred at narrow temperature range of 170° C to 250° C. Fluid inclusion data indicate that there is a progressive decrease of average temperature with paragenetic time. Mineralization stages evolved from initial higher temperatures (> 320° C) to later lower temperatures (near 170° C). Each of these stages represents a separate mineralizing system, which cooled and abated prior to the onset of the next. The nearly linear relationship between homogenization temperatures and salinities of fluid inclusions from stages indicates a history of progressive cooling and dilution of ore-forming fluids.During the early to main mineralization of ore stage the boiling of hydrothermal fluids led to high but variable salinities. Later cooling and dilution of fluids, which mainly deposited barren quartz in late ore veins in the deposits, resulted in the positive linear relationship between temperature and salinity. The relationship between homogenization temperature and salinities are shown in Figure 10.

 

2.2 Geochemical Survey

 Geochemical soil sampling grid system an area of 1 x 1 km with 50 m interval in Lowo Deba revealed anomalous zones of Cu, Pb, Zn, Au, Ag and Mo elements of various sizes and also identified two general geochemical anomalous zones in which different elements are overlap.The distribution of anomaly zone can be grouped into two combined anomaly i.e.  Au-Cu-Mo and Ag-Pb-Zn. First anomaly is Au-Cu-Mo is distributed in the middle of Lowo Deba prospect and concentrated in the phyllic and argillic andesitic tuff of Kiro Formation. This anomaly area also occupied by base metal and gold mineralization outcrops. The second combined anomaly of Ag – Pb – Zn is distributed in the middle and northeastern part of Lowo Deba (see Figure 6), concentrated within advanced argillic and argillic dacitic tuff of Tanahau Formation and partly in andesitc tuff of Kiro Formation,  showing the similar pattern to first group.Based on the statistical calculation (Table 2) this element distribution group shows the normal distribution pattern, while the probability plot was inferred to be derived from one population or one-mineralization source (Fig.11). From the histogram (Fig.11) analyses indicate the normal distribution and from the probability plot inferred derived from difference mineralization source. The presence of the first group, which is inferred, to be related with the mineralization process forming at high temperature/deep zone. While the appearance of the second group supposed to be related with mineralization process at low temperature (epithermal).

 

2.3 Geophysical Survey 

IP survey in Lowo Deba Prospect area is conducted of 12 lines (Fig.14), and from that lines interesting IP anomalies are found from line WA4 to line WA12 in electrode separation index of n=5 and n=7 as represents of illustrated lateral variation of chargeability and resistivity in depth of 75.0 m and 100.0 m approximately. The high chargeability anomaly for n5 spread along the river of east branch and west branch of Lowo Deba River as showing in figure 12 (c). The chargeability values for n5 have a range of 1.0 ~ 210.0 Msec. There are two high chargeability anomalies in this map. One anomaly lay along the main river of the central prospect area. This anomaly zone is divided by three high chargeability anomalies. The first anomaly is found at the west side of the main river in line WA4 and has high chargeability of 125.5 Msec. Also the second anomaly lay along Lowo Deba River in the central prospect area and has maximum value of 105.0 Msec. The third anomaly is found in northern part of prospect area as the east branch of Lowo Deba River and has a maximum chargeability value of 198.8 Msec.For n7, there are three high chargeability anomalies zone as seen in figure 12 (d). The first high chargeability anomaly is distributed in the central part of the prospect area along the Lowo Deba River and this anomaly has chargeability values from 20.0 to 420.0 Msec. In general this high chargeability anomaly spread from southwest to northeast and concentrate in the central part of the line WA6, WA7 and WA8 and in the northeastern part of the line WA10, WA11 and WA12. This anomaly still has potential of development toward northeastern part of this prospect area. Three high chargeability anomaly points of line WA4 have the maximum chargeability value of 142.7 Msec. Also second high chargeability anomaly is found in the western part of this area in the line WA8, WA9 and WA10 with chargeability value of 134.3 Msec. The third high chargeability anomaly is found in the west branch of Lowo Deba River in the northern part of this area with chargeability value of 91.0 Msec. Resistivity anomalies coincide with chargeability anomalies of n5 along the river, east branch and west branch of Lowo Deba River as showing in figure 13 (c). The resistivity anomaly values of n5 have a range of 0.0 ~ 4000.0 Ohm-m. Two resistivity anomalies are related with high chargeability anomalies. First resistivity anomaly is developed along the main river and to locate central part and east branch of Lowo Deba. And this low resistivity anomaly coincides with high chargeability anomalies of composed three spots in this site. In this resistivity anomaly resisvity value is less than 200.0 Ohm-m. The other high resistivity anomaly at the southern part of this map is found in east branch of Lowo Deba River at line WA4 as high resistivity anomaly. There are three low resistivity anomalies in index n7 on this map as showing figure 13(d). The first low resistivity anomaly is found in the central part of the prospect area along the Lowo Deba River including west branch and east branch. And this anomaly spread from southwest to northeast at line WA6, WA7, WA8, WA10, WA11 and WA12 with resistivity values of 0.0 – 150.0 Ohm-mAlso this low resistivity anomaly has more potential to develop to the northeastern part of this prospect area. The second low resistivity anomaly is found in the northern part of this area in the west branch of Lowo Deba River and has minimum value of 47.1 Ohm-m. The third low resistivity anomaly is found in the western part of this area in the line of WA8, WA9 and WA10 with minimum value of 42.6 Ohm-m. 

 

3. DISCUSSION 

During the whole survey of the mineral exploration project in Lowo Deba prospect area, documents and information on geology and mineral resources of the prospect area were compiled, while geochemical and geophysical data has been analyzed and interpreted. Regional and detailed geological survey, geochemical soil survey and geophysical prospecting were carried out to select the target area for drilling survey.Cu-Pb-Zn mineralization and geochemical anomaly zones were identified in Tertiary volcanic/intrusion and pyroclastic rocks of the survey area. The main anomalous of Au-Cu-Mo is widely distributed in the middle of prospect area. The anomalous zone is occupied by phyllic-argillic andesitic tuff and associated with gold and base metal mineralization outcrops. Fluid inclusion study indicates that fluid evolved from 320⁰ C to 170⁰ C.Geophysical IP prospecting found the area, which is most significant anomaly in line WA7 with chargeability value of 405.7 Msec and resistivity value of 37.7 Ohm-m.According to supported data including geology, geochemical and geophysical survey lets to predict that mineralization type supposed to be epithermal and massive sulphides. The high chargeability value suggests presenting the blind ore deposits below the surface. Some bore holes will be proposed to confirm the present of blind deposit.

 

4. CONCLUSSION

In Lowo Deba prospect, most of base metal mineralization was hosted by phyllic – argillic andesitc to dacitic tuff of Kiro Formation and Tanahau Formation and intrusive of granodiorite with the occurrences of structure control of epithermal type or massive sulfide type. This evidence supported by indication of fluid inclusion study results, geochemical anomalous of base metal and gold and geophysical IP method resulting anomalous zones of high chargeability and low resistivity.

 REFERENCES

1. Ahrens, L.H., 1954. Lognormal distributions of the elements. Geochim. Cosmochim. Acta 5, p. 49 – 73.

1. Franklin et al, 1999, Eksplorasi Logam Mulia dan Logam Dasar di Daerah Wai Wajo dan Sekitarnya Kabupaten SIKKA – Nusa Tenggara Timur. Proyek Eksplorasi Bahan Galian Mineral Indonesia. SubDirektorat Eksplorasi Mineral Logam, Direktorat Sumberdaya Mineral, Bandung.
2. Franklin et al, 2002, Inventarisasi Endapan Molibdenum dan Logam Dasar Serta Mineral Logam Ikutannya di Daerah Wai Wajo Kabupaten SIKKA Provinsi Nusa Tenggara Timur, Proyek Eksplorasi Bahan Galian Mineral Indonesia. SubDirektorat Eksplorasi Mineral Logam, Direktorat Sumberdaya Mineral, Bandung.
3. Hamilton, W.B., 1979, Tectonics of the Indonesian region. Prof.Paper 1078, U.S.Geol.Surv. Washington, DC, 345 pp.
4. Hedenquist, J.W., 1996, “Hydrothermal System in Volcanic Arcs”, Mineral Resources Department, Geological Survey of Japan, Tsukuba, Japan.
5. Hendaryono, 1999, Geologie de I’ile de Flores . Apports a l’etude de la geodynamique de l’archipel indonesien oriental. 200 p. ISBN 2-904431-21-7. Resume Francais, indonesien.
6. J.C, Carlile; A.H.G.Mitchelle, 1994, Journal of Geochemical Exploration 50. 91 - 142 pp.
7. J.V. Lawless, P.J. White, I. Bogie, Important Hydrothermal Minerals and Their Significance. Kingston Morrison Mineral Services, Nov 1994.
8. Katili, J.A., 1974, Geologi Enviornment of the Indonesian Mineral Deposit., publikasi Teknik seri Geologi Ekonomi No.7, Direktorat Geologi.Lepeltier, C., 1969. A simplified statistical treatment of geochemical data by graphical representation. Econ. Geol., v.6 p. 538 – 550.
9. Nishimura.S, Y.Otofuji, T.Ikeda, E.Abe, T.Yokoyoma, F.Kobayashi, S.Hadiwisastra, J.Sopaheluwakan, F.Hehuwat, 1981, Physical geology of the Sumba, Sumbawa and Flores Islands, spec.Publ.2, Geol.Res.Dev. Centre. Bandung, p.111.
10. N. Suwarna, S.Santosa, Koesoemadinata., 1990, Geologi Lembar Ende 1:250.000, Nusa Tenggara Timur., Pusat Penelitian dan Pengembangan Geologi Bandung.
11. Parasnis D.S, 1962, “Principle of Applied Geophysics”, Chap & Hall Ltd., UK.
12. Priatna B., et al., 2000, “Laporan Eksplorasi Geofisika Mineral Logam di Daerah Wai Wajo, Sikka, Flores, NTT”, PEBGMI – DSM.
13. PT.Nusa Lontar Mining, 1987, Contract of Work, First Relinquishment Report, Nusa Tenggara Timur, Indonesia (9757).
14. Sinclair, A.J., 1976. Application of Probability Graphs in Mineral Exploration; Ass. Explor. Geochem., Spec. Vol. 4, 95 pp.
15. Sutrisno et al., 2001, “Laporan Penyelidikan Geofisika Tematik di Daerah Sungai Mera, Kabupaten Sikka, Flores, NTT”, PIEBGMI – DIM.
16. Telford W.M., et al., 1976, “Applied Geophysics”, Cambridge Univ. Press, Cambridge.
17. Tudor, A, 1999, First Relinguishment Report and Upgrade from general Survey     Period to Exploration Period, Internal Flores Barat Mining (FBM) report.
18. Tukey, J.W., 1977. Exploratory Data Analysis. Addison-Wesley, Reading, Mass. 506 pp.

 

Fig.2 Regional Geological map of Wai Wajo and its surrounding

Fig.3 Geological map of Wai Wajo (Lowo Deba prospect)

Fig.4 Composition of volcanic rocks from Wai Wajo area

Fig.5 Main direction of joint measurement in Lowo Deba

Fig.6 Mineralization-alteration and geochemical anomaly map of Lowo Deba area

Fig.7 Mineralized Quartz vein from Lowo Deba

Fig.8 Microphotograph from sample KWA-13/A showing pyrite and chalcopyrite

Table 1. Mineralogy and fluid inclusion data from Wai Wajo/Lowo Deba

Sample No.	Mineralogy	Host mineral	P.	S.	Th(°)	Tm(°)	Eq.wt. % NaCl
KWW-1/RF	 Py+gn+sp	gr.quartz	P (30)	Â	201° - 324°	-5.0°-1.0	4.2-10.6
KWW-2/RF	 Py+cpy+gn	m.quartz	P (31)	Â	209° - 308°	-0.8°-1.6	3.7-5.0
KWW-3/RF	 Py+gn	m.quartz	P (40)	Â	178° - 326°	-6.1°-3.0	7.3-12.4
KWW-4/RF	 py+cpy	gr.quartz	P (62)	Â	177° - 320°	-6.0°-1.0	4.1-12.2

Abbreviations: py, pyrite; cpy, chalcopyrite; gn, galena; sp, sphalerite; gr, grey; m, milky; p, primary; s, secondary; eq, equivalent; Th, homogenization temperature; Tm, melting temperature.Numbers in parentheses are the number of inclusions measured.

Fig.9 Histograms of homogenization temperatures of fluid inclusions
in the main mineralization stage quartz from Wai Wajo area

Fig.10 Plots of homogenization temperatures versus salinity for primary Inclusions in the main mineralization stage quartz from Wai Wajo area

 

Fig.12 Distribution of chargeability in Lowo Deba Prospect in index n5 and n7

Fig.13 Distribution of resistivity in Lowo Deba Prospect in index n5 and n7

 

Fig.14 Geophysical IP prospecting in Lowo Deba area

Table 2 Statistical calculation of geochemical soil in Lowo Deba

BLOCK A WAI WAJO AREA	Element	Max	Min	Mean	BackGround	Anomalous			Combined Anomalous
						Weak	Moderate	Strong	 First anomalousAu – Cu  – MoAndSecond anomalousAg – Pb – Zn    Â
	Au (ppb)	32	1	4	1	2.07 < Au < 6.09	6.09 < Au < 17.28	Au > 17.28
	Ag	3	0.25	1	1	0.75 < Ag < 1.24	1.24 < Ag < 1.91	Ag > 1.91
	Cu	820	5	70	14	33.3 < Cu < 97.58	97.58 < Cu < 460.6	Cu > 460.6
	Pb	227	4	28	12	22.92 < Pb < 40.44	40.44 < Pb < 108.24	Pb > 108.24
	Zn	2546	32	239	77	164.78 < Zn < 378	378 < Zn < 937.09	Zn > 937.09
	Mo	17	1	2	1	1.24 < Mo < 3.5	3.5 < Mo < 8.05	Mo > 8.05

ARTKEL TERKAIT