Boda and Boda Two drilling results
On 18 December 2020, 8 March and 3 May 2021, Alkane reported the assay results of an additional 15 diamond drill holes (denoted DD) and an additional one reverse circulation (RC) hole at its Boda, Boda Two and Kaiser (Duke) prospects at its Northern Molong Porphyry Project. The drilling is part of a 30,000m diamond and reverse circulation core exploration programme that began in July 2020 to test the dimensions and extensions to the large, low-grade mineralised envelope at Boda, as well as any internal high-grade zones.
A summary of the 14 holes drilled at Boda and Boda Two is as follows:
Exhibit 7: Boda diamond drill hole assay results
|
From (m) |
To (m) |
Average/aggregate intercept (m) |
Average gold grade (g/t) |
Average Cu grade (%) |
Previously announced DD results |
|
|
760.5 |
0.29 |
0.13 |
Previously announced RC results |
|
|
303.3 |
0.17 |
0.10 |
KSDD014 |
436.0 |
915.0 |
419.0 |
0.21 |
0.03 |
KSDD028 |
120.0 |
1,088.0 |
839.0 |
0.38 |
0.17 |
KSRC033D |
0.0 |
878.0 |
612.0 |
0.24 |
0.11 |
KSDD017 |
11.0 |
914.0 |
338.0 |
0.24 |
0.12 |
KSDD018 |
0.0 |
897.0 |
566.0 |
0.21 |
0.11 |
KSDD021 |
106.0 |
981.8 |
775.8 |
0.14 |
0.10 |
KSDD024 |
16.0 |
1,896.0 |
461.0 |
0.20 |
0.04 |
KSDD015 |
6.0 |
1,249.1 |
1,243.1 |
0.18 |
0.12 |
KSDD016 |
30.0 |
1,160.0 |
501.0 |
0.19 |
0.18 |
KSDD019 |
12.0 |
1,105.0 |
611.0 |
0.22 |
0.10 |
KSDD023 |
15.0 |
1,323.0 |
630.9 |
0.24 |
0.03 |
KSDD029 |
620.0 |
1,107.0 |
220.3 |
0.22 |
0.14 |
KSDD030 |
116.0 |
1,724.0 |
1,489.1 |
0.15 |
0.10 |
KSDD031 |
645.0 |
1,238.0 |
407.2 |
0.77 |
0.31 |
New DD results |
|
|
654.0 |
0.24 |
0.12 |
New RC results |
|
|
612.0 |
0.24 |
0.11 |
All DD results |
|
|
705.1 |
0.26 |
0.12 |
All RC results |
|
|
331.4 |
0.19 |
0.10 |
All holes |
|
|
590.9 |
0.25 |
0.12 |
Source: Alkane Resources, Edison Investment Research
Note that, for the purposes of Exhibit 7, multiple intersections have been amalgamated and grades averaged according to the width of the individual intersections. In general, it may be seen that the 14 new holes reported widths of mineralisation that were consistent with (albeit slightly less than) those of previous diamond drill holes at slightly lower grades, but which were still wider and higher grade than the RC widths and grades previously reported.
Analysis and interpretation of Boda and Boda Two drill results
Three drill holes (KSDD017, KSDD018 and KSDD024) were completed in the area between the southern extension of the Boda mineralisation shell and the northern extension of the Boda Two prospect. One drill hole (KSDD021) tested the southern extensions to the Boda Two prospect and two (KSDD023 and KSDD030) defined a gold-rich pyrite zone on the eastern margin of a new zone of extensive copper-gold porphyry mineralisation. Two further holes (KSDD029 and KSDD031) were designed to intersect the north-west structural trend and test down plunge, on the reverse angle, of the high-grade breccia identified by holes KSDD007 and KSDD028. Three further holes (KSDD015, KSDD016 and KSDD019) continued to intersect extensive zones of gold-copper mineralisation with increasing molybdenum grades flanking the potassic alteration (see Exhibit 8, below).
Exhibit 8: Boda prospect drilling update
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In general terms, holes KSDD017, KSDD018 and KSDD024 confirm and extend the mineralisation identified in reverse circulation holes KSRC032 and KSRC031, while hole KSDD021 largely confirmed the earlier (significant) results from hole KSDD022, which intersected a large pyrite shell comprising stringers and aggregates of pyrite within a sequence of propylitic altered basaltic andesites and monzodiorite sills and dykes. In both cases, it is surmised that the thick intersection of strong gold mineralisation with anomalous copper and pathfinder elements could be indicative of a distal component to a new, large fertile magmatic system (Boda Two). The same is also true of the intersection of significant molybdenum and copper mineralisation at a depth below 841m at hole KSDD024, which also suggests a zonation of metals around a deeper magmatic source to the system. Hole KSDD028 was significant in that it was designed to intersect the north-west striking orebody at approximately 90°. The hole, collared in outer propylitic alteration, intersected a gold mineralised pyrite-sericite shell for approximately 300m downhole, which zoned in to extensive calc-potassic alteration with gold-copper (Au-Cu) mineralisation centred around a high-grade Au-Cu breccia. The breccia shows apparent sulphide zonation with the upper intercepts more pyrite rich, zoning towards the centre and at depth to more chalcopyrite rich with increasing Au-Cu grades, with the high-grade mineralisation appearing to plunge steeply to the north-east, possibly vectoring towards a ’causative’ intrusion to the Boda system. Individual high-grade intersections encountered in hole KSDD028 included:
■
832m grading 0.38g/t Au, 0.17% Cu from 256m
•
including 266m grading 0.66g/t Au, 0.36% Cu from 764m
•
including 65m grading 1.98g/t Au, 1.13% Cu from 799m
•
including 25m grading 4.43g/t Au, 2.59% Cu from 838m
Subsequent drilling, in the form of holes KSDD029 and KSDD031, successfully tested and extended the sulphide cemented breccia identified by holes KSDD007 and KSDD028 down dip within the main north-west structural zone by 100m. KSDD031, in particular, successfully intersected the sulphide cemented breccia down dip with significant assay results of:
■
383.2m grading 0.80g/t Au, 0.31% Cu from 775m
•
including 204m grading 1.40g/t Au, 0.51% Cu from 776m
•
including 101m grading 2.47g/t Au, 0.83% Cu from 824m
•
including 70m grading 3.04g/t Au, 0.92% Cu from 829m
The breccia remains open and further drilling in this area is designed to test the structure at depth where its nature may change from chalcopyrite dominant to more copper-rich bornite dominant as well as testing for a possible ‘causative’ porphyry intrusion to the breccia and Boda system. Hole KSDD014 intersected the north-east extension of the low-grading Au sericite-pyrite halo and may need to be extended in due course to test for Au-Cu porphyry mineralisation north-west of Boda at depth.
In terms of Edison’s attempts to estimate a mineralised inventory at Boda and Boda Two, the results continue to demonstrate a complication whereby, almost without exception, the results from the RC holes demonstrate lower widths and grades than those from comparable diamond core drill holes.
Exhibit 9: Recent Boda and Boda Two DD hole assay results cf comparable earlier RC results
Recent hole |
|
Prior comparable hole |
Hole |
Intersection (m) |
Average gold grade (g/t) |
Average Cu grade (%) |
|
Hole |
Intersection (m) |
Average gold grade (g/t) |
Average Cu grade (%) |
KSDD017 |
338.0 |
0.24 |
0.12 |
|
KSRC032 |
503.0 |
0.10 |
0.11 |
KSDD018 |
566.0 |
0.21 |
0.11 |
|
KSRC031 |
239.0 |
0.06 |
0.09 |
KSDD024 |
461.0 |
0.20 |
0.04 |
|
KSRC031 & 032 |
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|
|
|
|
|
|
|
|
|
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|
KSDD021 |
775.8 |
0.14 |
0.10 |
|
KSRC037 |
385.0 |
0.10 |
0.11 |
|
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|
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|
KSDD022 |
394.0 |
0.53 |
0.02 |
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|
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|
KSRC033D |
612.0 |
0.24 |
0.11 |
|
KSDD007 |
1,197.1 |
0.54 |
0.25 |
|
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|
|
|
KSDD010 |
869.0 |
0.17 |
0.08 |
|
|
|
|
|
KSDD012 |
1,159.0 |
0.18 |
0.12 |
|
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|
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|
|
KSDD016 |
501.0 |
0.19 |
0.18 |
|
KSRC016 |
176.0 |
0.20 |
|
|
|
|
|
|
|
|
|
|
KSDD023 |
630.9 |
0.24 |
0.03 |
|
KSRC031 |
239.0 |
0.06 |
0.09 |
|
|
|
|
|
KSRC034 |
201.0 |
0.20 |
0.14 |
|
|
|
|
|
|
|
|
|
KSDD030 |
1,489.1 |
0.15 |
0.10 |
|
KSRC036 |
291.0 |
0.11 |
0.11 |
Source: Alkane Resources, Edison Investment Research
In general, the diamond drill holes (DD) demonstrate wider overall intersections than their RC counterparts, extending to greater depths at higher grades. Of note, within the context of this observation, is the fact that hole KSDD021 finished in mineralisation. This difference between RC and DD drill hole results may be attributed to a) the zonation of the system and b) the fact that the RC drill holes are testing the upper part of the system, where grades are anyway anticipated to be lower (as is typical of this type of porphyry system). In addition, some of the RC drill holes are pre-collars for subsequent diamond drill holes in order to reduce the overall cost of the holes. Note that four RC holes (KSRC031, KSRC032, KSRC037 and KSRC038) also finished in mineralisation and two of these (KSRC032 and KSRC038) will be extended by diamond tails at a later date.
Exhibit 10 updates our estimates of the potential mineralised inventory in the light of the 14 new drill hole results at Boda. As previously, in recognition of the difference between RC and diamond drill results, we have included two updated estimates: one based on the whole population of results and the other based on the results of the diamond drill holes only. The results are also compared with the resources disclosed by Newcrest for Cadia Ridgeway c 100km to the south (see Exhibit 11).
Exhibit 10: Edison estimate of the potential size of Boda mineralisation
Source of underlying data |
Edison |
Alkane Resources |
Newcrest |
Characteristic (units) |
Updated (all holes) |
Updated (DD holes) |
***Prior (all holes) |
***Prior (DD holes) |
Alkane est. dimensions |
High-grade pod |
Surface projection |
Cadia Valley Ridgeway |
Cadia Ridgeway underground actual** |
Strike (m) |
1,034 |
1,034 |
891 |
891 |
1,000 |
150 |
1,069 |
250 |
|
Ave est true width (m) |
271 |
315 |
243 |
348 |
400 |
100 |
521 |
150 |
|
Est surface area (Mm2) |
|
|
|
|
|
|
0.557 |
|
|
Ave est true depth (m) |
915 |
1,044 |
819 |
1,036 |
1,100 |
500 |
1,020 |
600 |
|
Est volume (Mm3) |
256 |
340 |
177 |
321 |
440 |
7.5 |
568 |
22.5 |
|
Est density (t/m3) |
3 |
3 |
3 |
3 |
3 |
3 |
3 |
3 |
|
Est tonnage (Mt) |
769 |
1,020 |
533 |
964 |
1,320 |
22.5 |
1,704 |
67.5 |
151 |
Est ave gold grade (g/t) |
0.25 |
0.26 |
0.26 |
0.29 |
0.25 |
|
0.2 |
|
0.49 |
Est ave copper grade (%) |
0.12 |
0.12 |
0.13 |
0.13 |
0.12 |
|
|
|
0.32 |
Est ave AuE grade (g/t) |
0.45 |
0.47 |
0.43 |
0.46 |
0.45 |
3.0 |
|
2.0 |
0.84 |
Est contained gold (koz) |
6,192 |
8,648 |
4,480 |
8,985 |
10,624 |
|
10,957 |
|
2,400 |
Est contained copper (kt) |
938 |
1,267 |
682 |
1,253 |
1,609 |
|
|
|
480 |
Est contained AuE (koz) |
11,127 |
15,314 |
7,322 |
14,211 |
19,090 |
2,170 |
|
4,340 |
4,925 |
Source: Edison Investment Research. Note: *Edison estimates; **From Newcrest reserve & resource statement, 31 December 2020; ***Conducted at prices of US$7,674/t Cu and US$1,840/oz Au. Updated gold equivalent inventory and grades calculated at US$1,787/oz Au and US$9,401/t Cu.
In the context of the above estimates, it is worth noting the like-for-like increase in the lower end of our estimate of the potential resource at Boda, as represented by the ‘Updated (all holes)’ column, primarily as a result of the increase in our estimate of the dimensions of the deposit (albeit at a slightly lower average grade, overall).
In broad terms, given the information available, our best estimate of the overall size of the Boda deposit is 769–1,704Mt at an average gold grade of 0.25–0.26g/t containing 6.2–11.0Moz Au (cf 4.5–12.3Moz previously) plus copper and containing a high-grade pod of in excess of 2.1Moz gold equivalent (AuE) at a grade above its 3.0g/t AuE cut-off.
Clearly such estimates are very far from being anything close to JORC code-compliant and experience would suggest they have an accuracy of approximately ±75%. Even at the bottom end of this range however, it would suggest a multi-million ounce gold deposit at Boda with a potential valuation (based on the US$24.08/oz average valuation of in-situ ounces calculated in our report Gold stars and black holes, published in January 2019) in the range A$0.34–0.60/share (cf A$0.24–0.67/share previously).
Concurrent with activity at Boda and Boda Two, elsewhere drilling is testing identified anomalies at Kaiser and an area about 5km in length to the south of Boda (denoted Boda Three), as well as other regional targets within the 15km monzonite intrusive corridor that extends from Boda to Finns Crossing defined by both the 3D-IP survey and existing Alkane data.
Of the 15 drill holes reported upon in December 2020, March and May 2021, one, KSDD027, related to Kaiser and was designed to test a conductive induced polarisation (IP) anomaly within the Duke Zone on the north-eastern flank of the Kaiser porphyry style mineralisation.
KSDD027 intersected two zones of gold-copper porphyry mineralisation with grades and alteration similar to Boda and significant assay results of:
■
360m grading 0.38g/t Au, 0.15% Cu from 0m
•
including 7m grading 0.90g/t Au, 0.26% Cu from 119m
•
6m grading 0.90g/t Au, 0.29% Cu from 204m
•
6m grading 1.71g/t Au, 0.24% Cu from 332m
■
442m grading 0.17g/t Au, 0.11% Cu from 422m
•
including 27m grading 0.31g/t Au, 0.13% Cu from 492m
•
58m grading 0.28g/t Au, 0.16% Cu from 735m.
Overall, we calculate that hole KSDD027 had an aggregate intercept of 360m at a grade of 0.38g/t Au and 0.15% Cu, which, although slightly narrower than the majority of the holes featured in Exhibits 7 and 9, is nevertheless also of a higher grade in terms of both gold and copper.
The orientation of the Kaiser mineralisation (including the Duke zone) appears, at first glance, to be somewhat more varied than that of the Boda and Boda Two deposits. Taken together with the other drill holes for which results are known and using the same methodology as for Boda and Boda Two, Edison calculates that the drilling conducted to date could indicate a deposit at Kaiser of c 28.2Mt at grades of 0.34g/t Au and 0.24% Cu (0.72g/t AuE) containing c 305koz Au and 67kt Cu. In this respect, it is worth noting that the intersections at Kaiser appear to be both narrower and to a lesser depth than those at Boda and Boda Two. As before, this estimate is self-evidently not JORC code-compliant and we estimate that the accuracy of such an estimate is ±75%.
To date, approximately half the number of holes have been drilled at Kaiser as have been drilled at Boda and Boda Two. As such, there is ample scope for Edison’s estimate of in-situ mineralisation at Kaiser to increase with additional drilling and an indication of the potential of the Duke zone is demonstrated by the fact that, in Alkane’s words, it ‘is currently interpreted from existing drilling to be approximately 250m wide, striking over 800m and open along strike and at depth.’ These dimensions may be compared with those in Exhibit 9 for an indication of the potential mineral inventory that may be hosted by such an orebody (ie of the same order of magnitude as that contained at Boda and Boda Two). Within this context, it is worth noting that, by varying our assumptions regarding the orientation of the Kaiser mineralisation, in particular, we are able to generate a potential inventory of 116.6Mt at grades of 0.34g/t Au and 0.24% Cu (0.72g/t AuE) containing 1,258koz Au and 276kt Cu (compared with which our other estimate of 305koz is 75.6% smaller). In the meantime, follow-up drilling is being undertaken to start testing in the very prospective 800m corridor between Boda and Kaiser and in which very little effective exploration has been conducted to date.
Northern Molong Porphyry Project background
The Northern Molong Porphyry Project is 100% owned by Alkane, covers c 115km2 of the northern Molong Volcanic Belt (MVB) and is around 80km to the north-east of its Tomingley Gold Mine, in central-west NSW (Exhibit 11).
Exhibit 11: Location of the Northern Molong Porphyry Project
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To date, Alkane’s drill results at Boda have demonstrated both a similar stratigraphic sequence as well as style of alteration and mineralisation to Newcrest’s Cadia Province mines 110km to the south, although it is also more structurally complex. Nevertheless, together, the Cadia Province mines host a JORC-compliant mineral resource estimate of 36.1Moz Au at a grade of 0.35g/t Au and 8.2Mt of copper at a grade of 0.26% Cu plus silver and molybdenum and produced 843koz of gold in FY20 at an AISC of US$160/oz Au (net of by-product credits) to generate US$991m in free cash flow.
The Northern Molong Porphyry Project now comprises four exploration licences, Bodangora, Boda South, Kaiser and Finns Crossing, within which Alkane has defined five magnetic anomalies interpreted to be intrusive complexes, Kaiser, Boda, Comobella, Driell Creek and Finns Crossing, all within a 15km north-west to south-east trending corridor (Exhibit 12) and all close to road, rail, gas and water infrastructure. Importantly, the Boda anomaly correlates with a historical induced polarisation (IP) survey completed by CRA Exploration (now Rio Tinto) over the Boda Intrusive Complex (BIC), which showed a strong high chargeable anomaly along the northern edge of the survey area coincident with the magnetic anomaly. As a result, Alkane has recently completed a 70-line kilometre IP survey over the 6km strike extensions of the BIC to generate further drilling targets.
Exhibit 12: Northern Molong Porphyry Project regional geology
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Four of these targets have now been drill tested: Kaiser, Boda, Comobella and Glen Hollow. Exploration has identified the margins of major monzonite intrusive complexes that provide the primary control for porphyry and epithermal mineralisation with significant intersections being reported along the western margin of both the Kaiser Intrusive Complex and the BIC. Specifically, gold mineralisation has been discovered at Kaiser, Boda and Glen Hollow (which is part of Comobella), with recent drilling identifying multiple phases of monzonite to monzogabbro intrusion that are plumbing a north-west structural corridor hosting extensive (calc-)potassic alteration and significant gold-copper mineralisation. In this case, the north-west orientation of the structural zones is significant in that similarly oriented structural zones are important controls to Macquarie Arc alkali gold-copper porphyry mineralisation such as the Lachlan Transverse Zone at the Cadia Valley (and Northparkes) deposits. Within this context, the alteration at Boda suggests the prospect is positioned in the upper parts of an alkali porphyry system with high-level epithermal gold veins observed in some of the drilling coincident with strongly pyritic zones, while deeper drilling has defined strong pervasive hydrothermal alteration that is dominantly calc-potassic (ie, a biotite+actinolite+epidote+magnetite+chalcopyrite±kspar±bornite mineral assemblage), phasing out to a more distal propylitic alteration (albite+epidote+chlorite+pyrite±chalcopyrite).