Hutti Greenstone Belt: Host to a world class gold deposit
Hutti Maski Greenstone belt is one of the most important Archaean gold bearing belts in India. The Auriferous tracts of Hutti greenstone belt are remarkably similar to the classic Archaean Superior Craton in Canada, the Yilgarn Craton in Western Australia and the Kolar greenstone belt in India. The Hutti-Maski belt hosts world class Hutti Gold deposit that is being presently mined by The Hutti Gold Mines Limited. Gold mining activity in the belt has been known since pre-Ashokan time, about 3000 years ago. Modern gold mining commenced in the Hutti area around 1947.
The Hutti Gold Mine has so far produced about 2 million ounces while remaining ore reserves (proven and probable) are believed to be 9.25 million tonnes of ore grading 5.62g/t up to 841 metres depth.
Exploration was carried out by under two Reconnaissance exploration Licences (RPs) covering a total area 851 sq. km of the most prospective part of the Hutti belt.
Hutti North RP Block:
DGML through its subsidiary DESPL explored an area of 501.48 sq.kms in the Hutti North RP Block by means of modern methods of exploration. The summary of Exploration carried out is furnished in the table:
|SUMMARY OF EXPLORATION WORK CARRIED OUT IN|
|HUTTI NORTH RP BLOCK|
|SL NO||TYPE OF EXPLORATION||UNIT||QUANTUM|
|2||GEOLOGICAL MAPPING (1: 2000 AND 1:5000 SCALE)||SQ.KMS||500|
|3||GROUND GEOPHYSICAL MAGNETIC SURVEY||LINE KMS||145|
|4||GROUND GEOPHYSICAL IP SURVEY||LINE KMS||9|
|5||SAMPLING AND ANALYSIS|
|A. ROCK CHIP||Nos||953|
|C. TERMITE MOUND SAMPLES||Nos||85|
|D. SOIL SAMPLES||Nos||819|
|E. BED ROCK GEOCHEMICAL SAMPLES||Nos||3980|
|F. RAB DRILL SAMPLES||Nos||598|
|G. RC DRILL SAMPLES||Nos||1319|
|H. DIAMOND CORE SAMPLES||Nos||387|
|A. RAB DRILLING (18 DRILL HOLES)||862.5|
|B. RC DRILLING (36 DRILL HOLES)||METRES||2186|
|C. DIAMOND CORE DRILLING (4 DRILL HOLES)||METRES||807.7|
Based on results of the geophysical and geochemical investigations, DGML completed 3850 metres of reconnaissance reverse circulation drilling (RC), RAB and diamond core drilling have been carried out. All the drill hole samples were analysed for gold and other associated elements. These studies led to defining 21 potential gold bearing blocks for detailed prospecting under Prospecting Licenses (PLs). Amongst these, Hutti North and Hirenagnur prospects are considered the most important. A total of 12 prospecting licenses (PLs) applications covering the 21 gold targets and 1 Mining lease (ML) application in Hirenagnur have been filed with the Karnataka State Government. The P.L. blocks identified are shown in the above figure.
Highlights of these prospects are presented below:
1. Hutti Mine North prospect
This block is located immediately north of the currently operating Hutti Gold Mine. Eight parallel gold bearing quartz-sulphide veins known as Reefs or lodes are known to exist in the currently operating Hutti Mines. These lodes were interpreted to extend northwards into our exploration ground for about 2.0 km beyond the northern boundary of the Hutti mines.
The objective of our exploration was to prove the extension of the lodes. Most parts of this prospect are under cover of black cotton soil, and hence, DGML adopted multi-parametric exploration techniques to trace mineralised zones. DGML’s exploration such as IP geophysical survey, Bedrock-geochemical sampling, Channel sampling, and limited drilling has resulted in tracing the extensions 5 significant zones of mineralization. The best finding was an extension of the New East Reef which has analysed upto 10.0 g/t gold and the extension of the Main Reef that has analysed upto 16.0 g/t Gold. Strike Reef was explored by DGML by limited drilling with positive results. All the inferred extensions are shown in the figure.
A PL application has been lodged over the prospect, grant of which will enable us to take up a detailed drilling programme needed to define the subsurface extensions and grades of mineralized zones.
a) Hirenagnur Prospect
DGML considers Hirenagnur prospect as one of its best discoveries which are located 5 kms southeast of Hutti Gold Mines. This prospect is an open-ended N-S trending zone revealed initially by a single rock chip sample analyzing a gold value of 7.13 g/t. Systematic exploration by means of geochemistry, ground geophysics, RC drilling and structural mapping has established a mineralized system of 2 kms length over a width of nearly 50 meters.
Analysis of 473 bedrock samples collected at 10 m intervals along E-W profiles spaced 40m apart revealed the presence of highly anomalous gold values of 56 to 461ppb in banded iron formation. Further, follow-up rock chip samples showed values of up to 7.78 g/t gold. Channel sampling across the 50m wide zone, identified sub-parallel mineralized zones of 2 to 15 m width with gold grades of 1 to 3 g/t.
DGML also carried out a detailed ground magnetic survey to explore strike extension of the mineralization towards north and south. The magnetic survey was successful in tracing a high magnetic anomaly for a length of 3.2 km coinciding with the main Hirenagnur mineralization and its extension towards north and south. Hirenaganur prospect is a structurally controlled mineralization.
These coincident geophysical and geochemical anomalies encouraged drilling. A total of 1078 m of shallow RAB and RC drilling were successful in defining 4 parallel gold bearing zones having a cumulative strike length of 1030m.
Some of the best drill intercepts are furnished below:
|Drill hole No.||Width (m)||Grade(g/t)|
The details of the four mineralised zones are:
- Footwall magnetite-gold lode: 500m long with 7.5m av. width @ 3.34g/t av. gold.
- Central magnetite’s-gold zone: 280m long with 6.23m av. width @ 2.12g/t av. gold.
- Hanging wall sulphide-gold zone: 250m long with 8.63m av. width; 4.34g/t av. gold.
- A single intersection lode west of (c): 25m long with 6m av. width; 3.52g/t av. gold grade.
The drill hole data was processed by using Datamine Geological software which shows that all the 4 ore zones are open along strike and depth that would be investigated by detailed drilling. The data generated also suggests the possibility of open-pit mining of the Hirenagnur ore body.
Hirenaganur prospect is a structurally controlled mineralization. Therefore, the continuity of gold bearing structures is expected up to several hundred metres. Applications have been filed for both PL as well as a Mining Lease. Detailed drilling will follow the grant of prospecting licence over this prospect.
Ore beneficiation studies of Hirenagnur ore was carried out at the India Bureau of Mines, Bangalore. The studies indicate that the ore is free milling and 91% of gold recovery was achievable by carbon –in- leach technique. Pre-treatment of the ore can result in 97% recovery. DGML has estimated an inferred resource of 200,000 ozs averaging 2.72 g/t Au.
A Prospecting Licence application has been lodged, upon a grant of which Deccan Gold will undertake further detailed drilling to test the deeper extensions of the zones.
b) Uti mine lodes- Southern and Northern continuity
The Uti Mine is owned and operated, as an open pit mine, by the Hutti Gold Mines Ltd. GSI’s drilling helped to trace the southern continuity of the gold-bearing reefs beyond the lease hold of the Uti mine. Structural mapping revealed that the Uti mine is controlled by a major discordant structure. This structural control encouraged us to investigate the southern and northern continuity of the Uti mine. Preliminary drilling was directed at establishing the southern continuation.
Bedrock sampling at 20 m intervals along 9 profiles southwest of Uti mine and along 3 profiles north of the mine have revealed gold anomalous zone in strike continuity of Uti mine lodes for about 3.5 km to the SW and also towards the north.
609m of reconnaissance drilling confirmed the strike continuity of gold lodes to the south. One of the lodes showed gold in the range of 0.82 to 1.4 g/t over widths ranging from 1 to 5m; a second lode yielded 1.34 to 1.72 g/t gold over 1 to 2m width; one more intersection analyzing 3.49 g/t gold over 4m was traced to yet another lode. Detailed drilling is called for to establish the full potential of the Uti south and North prospects.
c) Uti Temple Prospect
Old diggings by ancient miners and our recent channel sampling have revealed the existence of three sub-parallel mineralized zones in area 1.2 sq km west of the HGML’s Uti mine. Surface samples have given high gold values of up to 22.94 g/t and 40.38 g/t gold. Bedrock geochemical sampling has indicated an anomalous gold-bearing zone which is 1200m long and 80m wide.
d) Chinchergi Prospect
Chinchergi prospect located some 15 km east of Hutti Gold Mine is an area of extensive ancient mining. This prospect is an excellent exploration target defined by DGML as a result of extensive geochemical exploration, geological mapping, ground magnetic survey and limited Reverse Circulation drilling. DGML targeted a part of the major WNW trending Chinchergi- Amareshwara lineament between Chinchergi Prospect and Wandalli Prospect.
Initial reconnaissance rock chip samples analysed 5.59 g/t, 8.33 g/t, 9.92 g/t and 12.73 g/t within this prospect. Channel sampling revealed 1 to 2m wide narrow lodes analyzing 1.18 g/t to 4.38 g/t. Systematic bedrock geochemical sampling was carried out involving 22 profiles and 1500 samples. The exploration has resulted in delineating two geochemical gold anomalies south and west of Chinchergi Prospect. The 80 to 200 metres wide southern anomaly indicates the presence of a number of quartz veins and hydrothermal alterations. Also observed was another similar vein- alteration anomalous zone, 75 to 100m wide, west of Chinchergi.
Eight widely spaced reconnaissance reverse circulation bore holes were drilled covering a strike length of 3.7 km. One borehole (DCH-1) intersected an ore zone with an average gold value of 1.41 g/t over 8m width. Important intersections in two other boreholes include 4m x 1.1 g/t (DCH-7), 5m x 2 g/t (DCH-2). These results are considered encouraging to warrant further drilling on close spaced grids.
e) Bullapur Prospect
This is one of the recently discovered prospects in the Hutti belt located outside of the GSI-explored area of ancient gold workings. In the course of geological traversing along the major structural discontinuity south-east of Chinchergi village, a new zone of mineralization was located close to Bullapur village. The mineralized zone comprises a series of quartz veins disposed of as N-S plays from a narrow ENE trending shear zone. One of the veins showed a number of visible gold grains on panning. A rock chip sample yielded a good value of 6.53 g/t gold. The area deserves to be investigated in detail under a Prospecting Licence.
f) Yatkal Prospect
Yatkal Prospect is situated along the southern margin of the North Huttti R.P. Block and gold is found in the granites intruding the Hutti volcanic belt. Stream sediment sampling initially drew attention to the area as a possible source of the gold anomaly. In several termite mound samples, more than 100 ppb gold, a highly anomalous geochemical value, was noted. This prompted a systematic soil grid geochemical survey involving a collection of 819 soil samples at 20 m interval along profiles 40m apart. Gold content of greater than 50 ppb was taken to define the anomaly.
Two distinct zones of gold mineralization emerged following the soil sampling. A 900 m long, 150 m wide NE trending anomalous zone in the western part and a NW trending 400 m long narrow zone in the eastern part. The western anomalous zone shows sulphide rich granodiorites with 5 parallel zones of quartz veins. The NW trending eastern zone is a zone of highly silicified pink granite with amphibolite patches traversed by quartz veins, disseminated with chalcopyrite and pyrite. Rock chip sampling has revealed anomalous gold content in several samples with best values ranging from 1 to 32.05 g/t. Detailed sampling by trenching and drilling is warranted under a Prospecting License.
Update on SLPs in the Supreme Court (Hutti Belt):
A Special Leave Petition (SLP) in the Hon’ble Supreme Court of India, was filed by DGML, against the Order dated 3 April 2012 passed by the Hon’ble High Court of Karnataka regarding the reservation of Hutti Belt areas in favour of HGML. DGML’s SLP was admitted in the Hon’ble Supreme Court on 16-7-2012 and the Hon’ble Court has further observed that the decision to be made by the Central Government shall be subject to the outcome of the present SLP.
DGML would like to summarize the back ground information regarding the legal aspects:
- Karnataka Government’s proposal to reserve the entire Hutti-Maski Belt in favour of Hutti Gold Mines is being challenged by DGML. The company filed a revision petition application with the Ministry of Mines, Delhi to adjudicate on the Karnataka Government’s reservation proposal.
- The Revision Authority (Tribunal), Ministry of Mines, Government of India passed a Final Order on 22 October, 2010 whereby it rejected the recommendation of the State Government of Karnataka to reserve the areas in favour of Hutti Gold Mines Limited and directed the State Government of Karnataka to consider the pending PL applications of DESPL under the relevant law within a period of 100 days.
- Following this verdict, Hutti Gold Mines Limited filed a Writ Petition before the Hon’ble High Court of Karnataka challenging the aforesaid Final Order dated 22 October 2010 passed by the Revision Authority (Tribunal) Ministry of Mines, Government of India.
- The Hon’ble High Court of Karnataka passed an Order dated 18 February, 2011 quashing the Order dated 22 October, 2010 passed by the Revision Authority (Tribunal), Ministry of Mines, Government of India and further, the Hon’ble High Court directed the Ministry of Mines, Government of India to consider the recommendation of the State Government of Karnataka to reserve the areas in favour of Hutti Gold Mines Limited in accordance with law.
- The Ministry of Mines, Government of India (Central Government) rejected the recommendation of the State Government of Karnataka to reserve an area of 16,109 hectares in the Hutti Belt, Karnataka in favour of Hutti Gold Mines Limited, a State Government PSU and has instead directed the State Government to consider the pending Prospecting Licence applications of DESPL.
- Hutti Gold Mines Limited filed a Writ Petition in the Hon’ble High Court of Karnataka challenging the aforesaid decision of the MoM. Hon’ble High Court of Karnataka and vide its Order dated 3 April 2012 allowed the Writ Petition of Hutti Gold Mines challenging the Ministry of Mines, Government of India (MoM) Order dated 31 May 2011 rejecting the State Government of Karnataka’s recommendation for reserving the Hutti Belt areas in favour of its own PSU viz., Hutti Gold Mines Limited. Further, the Hon’ble High Court of Karnataka directed the MoM to take a fresh decision on the matter within 3 months.)
- It is to be noted that the Ministry of Mines also filed an SLP on 7th of September, 2013 against the Karnataka High Court Order.
- As regards the SLP filed by the Company, HGML has filed its Statement of Objections and the Company has filed a Rejoinder to the same in consultation with its Lawyers. The Company has also been served with copies of the SLP filed by the MoM and it is noted that the MoM’s stand is in support of the Company’s contentions, based on which the Company has filed a counter affidavit. We remain confident of the outcome restoring our rights over the Hutti Prospects.
- Due to delays in grant of PLs, DGML was unable to undertake further detailed exploration in the Hutti-Maski belt.
2. Prospects In South Hutti RP block
Ancient gold workings dating back to Ashokan time dot a 20 km long tract in the South Hutti belt which is marked by a major N-S trending shear zone designated as the “Central Shear Zone (CSZ)”. The tract was explored by us under a Reconnaissance Permit. This tract contains several promising prospects shown in Fig.8. The following targets have been chosen for intensive exploration based on highly encouraging gold values obtained during reconnaissance geological mapping and geochemical sampling which included analysis of 930 outcrop rock chip samples, 287 stream sediments and 389 bed rock samples. The exploration was successful in identifying four prospects worthy of detailed investigation, hence, these have been covered under PL applications which are in various stages of processing.
a) Tuppadhur-Buddini Prospect
A series of ancient pits and 6 inclined shafts are spread over a strike length of about 2.6 km in this prospect. Gold mineralisation is confined to the central shear zone and is generally found in quartz-ankerite veins with the wall rock showing intense chlorite and carbonate alteration. At Buddini, four parallel lodes have been identified. Extensive British time old workings occur along two of them – the Main and Mopla Lodes. Samples from mine dumps assayed up to 19.3 g/t gold. Detailed drilling will be undertaken once PL is granted for which our application is pending with the Government.
b) Maski Prospect
This prospect has all the signs of an important goldfield. Thirteen old workings were reported in this prospect in the early 1900s by the Hyderabad Geological Survey. M/S John Taylor and Sons developed one of these workings with a 35 m deep shaft, drove levels north and south and mined the ore of an average grade of 30 g/t gold. All of the diggings are now buried under the black cotton soil. Rock chip sampling, in the vicinity of these old diggings, has given some high gold assays, including 8.93 g/t from the sludge of a groundwater borehole; up to 11.6 g/t from a pit to the bedrock and up to 33.86 g/t from float samples. Based on these results, an auger-bedrock sampling programme was undertaken which revealed five broad gold anomalies. These results are to be investigated in detail under a Prospecting Licence.
c) Ashoka Prospect
The Ashoka Prospect (named after the great Indian emperor whose inscriptions are seen near Maski town) was a discovery happened during one of our stream sediment geochemical survey programmes. The prospect is defined by brecciated quartz-carbonate-haematite veins traversing fractured pink potassic granite. Rock chip sampling gave assays of 4.9 g/t gold and 0.63% copper. Reconnaissance geological mapping has revealed that the mineralized zone trends WNW, but the zone is covered under thick black cotton soil. Detailed trenching and geochemical soil sampling is planned prior to preliminary drilling.
d) Sanbal Prospect
Five sub-parallel zones of mineralisation have been identified in this prospect. Among them, Zone I consisting of highly folded quartz veins assaying up to 500 g/t Au. An open pit was developed by the Hutti Gold Mines Limited on Zone I, and about 2000t to of ore at a grade of 7.5 g/t gold was mined and processed. We plan to carry out detailed prospecting involving drilling to find the depth extensions of the high-grade gold ore shoots mined in the past and existence of additional ore shoots.