The Adanac porphyry molybdenum deposit is located north of Ruby Mountain and the headwaters of Ruby Creek which drains into Surprise Lake, about 23 kilometres northeast of the town of Atlin.
The Adanac/Ruby Creek deposit is a disrupted, ring-shaped occurrence formed late in the development of a localized plutonic complex. It is associated with granitic to quartz monzonitic rocks of the Late Cretaceous Surprise Lake Plutonic Suite, east of Atlin.
The Atlin area is underlain by deformed and weakly metamorphosed ophiolitic rocks of the Mississippian to Triassic Cache Creek Complex. These rocks include serpentinites and basalts as well as limestones, cherts and shales. The stratigraphic rocks are cut by two younger batholiths. North of Pine Creek, they are cut by a granodiorite to diorite intrusion known as the Fourth of July Creek batholith of the Middle Jurassic Three Sisters Plutonic Suite, and north and south of Surprise Lake they are cut by a Late Cretaceous granitic to quartz monzonitic intrusion known as the Surprise Lake batholith. The rocks are locally strongly faulted and the Adanac deposit is located near the intersection of two major, syn- to post-mineral fault systems.
The deposit location is partially controlled by, and is partially offset by, the Adera fault system which trends from northeast to southwest down Ruby Creek and defines much of the southern boundary of the Fourth of July Creek batholith. The deposit is also controlled by the Boulder Creek fault system. This runs due north up Boulder Creek and cuts across the head of the Ruby Creek drainage. The Boulder Creek fault appears to have helped localize emplacement of the deposit, which is intimately associated with late stage porphyritic and aplitic plutonic rocks intruded into in a marginal phase of the Surprise Lake batholith.
The Adanac deposit underlies the valley floor near the head of Ruby Creek. It is largely buried and has very little surface expression. There is little outcrop in the lower part of the valley and molybdenite is only rarely found in float and/or in veins in outcrop in the bed of the creek. The geology underlying the valley floor is largely derived from drill data.
The Adanac area is underlain by two separate pulses of plutonic rock. The first pulse, which includes the contact phase between the two batholiths, consists of a highly variably textured unit that grades from "Coarse-grained Quartz Monzonite" (CGQM) south of the Adera fault through a number of texturally transitional phases including "Transitional and/or Hybrid Coarse-grained Quartz Monzonite" (CGQM-T; CGQM-H) and "Crowded Quartz Feldspar Porphyry" (CQFP) to "Sparse Quartz Feldspar Porphyry" (SQFP) upward and outward from the deposit. The latter is well exposed north of the Adera fault, near the diorite contact.
Coarse grained quartz monzonite is weakly to moderately deformed, and consists of pink to grey equigranular, coarse grained (0.5 to 3.0 centimetres) quartz monzonite consisting of equal amounts of orthoclase, plagioclase and grey quartz. The feldspar is commonly seriate and, locally, includes a small amount of fine grained (2 to 4 millimetres) matrix. Coarse grained quartz monzonite grades to sparse quartz feldspar porphyry with increase in matrix content, and increased isolation of constituent "phenocrystic" crystals, particularly orthoclase and quartz.
The first phase also includes a distinctive "Mafic Quartz Monzonite Porphyry" (MQMP) unit that is present east of the deposit. This distinctive grey rock type has a seriate (1 to 4 millimetres) locally porphyritic texture. It is composed largely of chalky white plagioclase, disseminated biotite and phenocrysts of ragged plagioclase and lesser quartz. These rocks were fractured and deformed prior to emplacement of the second pulse of magma.
There are three main mappable phases to the second pulse. They include "Crowded Quartz Monzonite Porphyry" (CQMP); "Sparse Quartz Monzonite Porphyry" (SQMP) and "Fine-grained Quartz Monzonite" (FGQM). The crowded porphyry has an average of 50 per cent (2 to 6 millimetres) subhedral to euhedral plagioclase, orthoclase, quartz and biotite phenocrysts in an aphanitic matrix. The sparse variety is similar, but has fewer (10 to 30 per cent) phenocrysts. The porphyries are fresher and generally less deformed than the surrounding rocks and they have a much finer, more chilled matrix than the sparse quartz feldspar porphyry described above. The porphyries cut out the older rock units. They are exposed, locally, in the floor of the valley and they are found in the subsurface, under the valley floor, upstream. In this locality, coarse grained quartz monzonite and its variants are intruded by a buried cupola of sparse quartz monzonite porphyry. Its shape has strongly influenced the locus of mineralization, as shown by Placer Development's 0.06 per cent and 0.1 per cent molybdenum assay contours at 1448 metres elevation. Mineralization surrounds the buried cupola and, to a lesser extent, covers it.
The fine grained quartz monzonite is a variably textured "aplite" that intrudes coarse grained quartz monzonite (and also its variants) and mafic quartz monzonite porphyry above and around the sparse and crowded porphyry intrusions. The rock type is not exposed on surface, but it is well documented as forming a series of 0.05 to 10 metres thick, approximately flat lying, structurally controlled sills in the "higher-grade" (northeastern) portion of the deposit. The sills are well exposed in Kerr Addison's crosscut, where some of the rock immediately north of Ruby Creek can only be described as plutonic breccia. The fine grained, aplitic dikes are found elsewhere around the buried sparse-porphyry cupola; however, they are generally less frequent and smaller, and occur as narrow dikelets.
In addition to these rock types, recent drilling at the southwest end of the deposit has located a "Megacrystic Feldspar Porphyry" (MFP) unit in the subsurface. This is not well constrained; however, it appears to be a relatively young phase of the quartz monzonite intrusion. It consists of rare to abundant large (>10 millimetres) euhedral orthoclase phenocrysts in a chilled matrix. Another notable feature throughout the deposit is the presence of coarse grained quartz feldspar pegmatite. This is not abundant. However, it is widespread as small dikes and structurally controlled sills.
The Adera fault is a composite structure that dips steeply to the northwest. It is "normal" in character and appears to have downdropped (to the north) the northwestern part of what was originally a ring-shaped deposit formed above and around a sparse porphyry intrusion. Mineralization has been found in the coarse grained and related rocks northwest of the southernmost strand of the Adera fault. However, it has not been found in (probably similarly aged) sparse quartz feldspar porphyry and related rocks further north. These rocks, which are well exposed in the creek canyon below Molly Lake, contain abundant barren quartz veins and disseminated pyrite. They are gossanous, but barren.
The rocks at Adanac are, for the most part, fresh and much of the alteration that is observed is secondary, associated with fluids that circulated during post-mineral faulting. However, there is a small amount of primary alteration. It occurs as sill-like zones of intense silicification intermixed with bodies of aplite in the "higher-grade", northeastern part of the deposit, and as intermittent feldspar envelopes and flooding around individual mineralized quartz veins throughout the deposit. In one locality, the silicification can be shown to pre-date both intrusion of aplite and emplacement of mineralized quartz veins.
Fractured rocks near post-mineral faults, such as the Adera, have commonly undergone secondary alteration. They are either weakly or strongly altered to a mixture of sericite, carbonate, clay and chlorite (without addition of secondary quartz). The altered rocks become soft and friable and early (1969-72) core recoveries dropped. Major faults commonly include breccias cemented by grey gouge of similar composition, with or without smeared-out molybdenite. Some of the altered rocks contain fluorite veins. Work by Placer Development in 1980 shows that most of the light coloured clay is predominantly montmorillonite; however, the grey clay in the main Adera fault zone consists largely of kaolinite.
The Adanac/Ruby Creek deposit consists of a stockwork of veins of molybdenite and quartz-molybdenite found in all the principal rock types. However, it is best developed in the early stage plutonic rocks (mafic quartz monzonite porphyry and coarse grained quartz monzonite and its variants) that overlie and surround the buried sparse quartz monzonite porphyry stock under the Ruby Creek valley. The veins are most commonly without other metallic phases, although pyrite is found locally and chalcopyrite has been observed. The veins locally contain traces of scheelite, orthoclase, fluorite, biotite, sericite and carbonate.
Mineralization postdates emplacement of fine grained quartz monzonite in the "higher-grade" zone located on the northeast side of the deposit. There, there appears to be a crude positive correlation between presence of dikes and sills and amount of mineralization observed. However, the same relationship does not hold on top of the cupola or in the southwestern side of the deposit. The deposit consists of a mineralized blanket that covers the sparse quartz monzonite porphyry stock and dips off in all directions.
The mineralization commonly consists of sulphide veins, as coatings on quartz-free fractures and as coarse and fine rosettes and blebs in both smokey and lesser clear quartz. It also occurs as streaks and smears in deformed rock and may, locally, be enriched in fault zones. In the "higher-grade" zone explored by Kerr Addison, much of the mineralization is in horizontal to subhorizontal veins and fractures from 1 to 5 millimetres wide that are interspersed with veins that are considerably wider, up to 20 millimetres wide. The near-horizontal vein set is commonly cut by narrow 1 to 3 millimetre quartz veins that are oriented at a high angle to the (vertical) core axis. Both vein sets are mineralized and blebs of molybdenite commonly occur at the intersection of crosscutting veinlets.
The near-horizontal vein set is locally extremely well mineralized. Veins exposed through underground development in the 1970s show that coarse rosettes of molybdenite up to 30 millimetres in diameter formed in the plane of the vein, and that the spacing between the rosettes is variable, causing a pronounced "nugget effect" in drilling.
The crowded and sparse porphyries underling the "higher-grade" zone are cut by narrow (1 to 3 millimetres) mineralized quartz veins and fractures that also occur at both high and low angles to the (vertical) core axis. These veins and fractures commonly contain fine grained to powdery molybdenite. There are fewer high-grade rosettes formed at depth.
In December of 2007, Adanac Moly Corp. announced updated measured and indicated combined resources of 212,907,000 tonnes grading 0.063 per cent molybdenum and updated proven and probable combined reserves of 157,685,000 tonnes grading 0.058 per cent molybdenum. Both estimates were based on a 0.04 per cent molybdenum cut-off (Press Release - December 6, 2007; www.adanacmoly.com).
In 1905, the Adanac (Ruby Creek) deposit was discovered but had limited exploration prior to 1966, when different parts of it were staked by Adanac Mining and Exploration Limited and Canadian John's Manville Limited. Adanac Mining (no relation to Adanac Moly Corp.) acquired the controlling interest the following year and drilled 80 holes for an aggregate length of 12,775 metres. In 1970, it optioned the property to Kerr Addison Mines Limited. Kerr Addison diamond drilled a further 47 holes for a total depth of 5626 metres and drove 589 metres of drift, 246 metres of crosscut and 281 metres of raise in the "high-grade" core of the deposit. It extracted 9545 tonnes of ore, primarily from six raises and processed them on-site to assess the significance of a well defined "nugget effect" caused by coarse-grained molybdenite. In 1972, Chapman, Wood and Griswold Limited completed a feasibility study and deemed the deposit uneconomic. As a result, Kerr Addison dropped its option. The following year, 1973, Climax Molybdenum Corporation of British Columbia Limited diamond drilled and/or deepened a further 9 holes for an aggregate depth of 2672 metres. It dropped its option and thereafter, the property remained dormant until metal prices improved in the late 1970s.
In 1978, Placer Development Limited optioned the property and initiated a full-scale technical and socio-economic evaluation. In 1979, it diamond drilled a further 6028 metres in 49 holes in and around Kerr Addison's proposed "initial pit" area, and the following year it drilled a further 27 holes with an aggregated depth of 4858 metres, in and around its "ultimate pit" area. Although Placer Development completed nearly all the work required for a feasibility study, it was never completed. In 1983, the price of molybdenum dropped sharply and the option eventually returned to Adanac Mining. Adanac Mining and Exploration Company defined reserves of 151 million tonnes grading 0.063 per cent molybdenum (Northern Miner - March 13, 1980).
The claims lapsed in the late 1990s and Adanac Gold Corporation (Adanac Molybdenum Corp.) (no affiliation with the original Adanac Mining and Exploration) staked the deposit in 2002. The company initiated a drill program in 2004 in order to gather data toward calculating a NI 43-101 compliant resource. The company diamond drilled 38 holes for an aggregate depth of 9087 metres.
In 2005, Adanac Moly Corp. conducted a major exploration program on the property. It diamond drilled 19 holes for an aggregate depth of 4984.1 metres in and around the main deposit, and percussion drilled 17 holes for a total depth of 249 metres lower down the valley. It also dug and sampled 81 backhoe pits as part of a study of surficial cover in the vicinity of its proposed millsite and tailings impoundment. Several of the holes indicate that the deposit extends beyond the current pit configuration. The company plans a diamond drill program in early 2006 to test the western extension for higher grade molybdenum potential.
In April 2005, AMEC Americas Limited (“AMEC”) established an NI 43-101 compliant combined measured and indicated geological resource for the deposit of 205,100,000 tonnes grading 0.062 per cent molybdenum at a cut-off grade of 0.04 per cent (Press Release - November 10, 2005).
In 2006, Adanac Moly drilled 16 holes for an aggregate depth of 3920.7 metres and submitted approximately 1300 samples analysis. Thirteen holes were angled through the proposed phase 1 pit of the deposit to test the significance of near-vertical veins, and to obtain samples for metallurgical test work. The remaining three were exploration holes drilled into, and beyond, the south wall of the proposed pit.
Between July 2007 and March 2008, Adanac Molybdenum Corporation conducted a major drill program on the property. Six holes were diamond drilled for an aggregate depth of 2433.4 metres in the main deposit area; an additional six holes for a total length of 1993.1 metres were drilled in the same area. A further ten "condemnation" diamond-drill holes totalling 2141.0 metres were drilled in the proposed mine site and tailings pond area.
As of 2009, the mineral resource estimate is stated as (www.adanacmoly.com):
Measured: 43,642,000 tonnes grading 0.078 per cent molybdenum
Indicated: 231,712,000 tonnes grading 0.065 per cent molbdenum
Total measured and indicated: 275,354,000 tonnes grading 0.067 per cent molybdenum.