The following key points apply to the Achmmach deposit mineralisation:
The Achmmach tin deposits occur within metamorphosed shales, siltstones and sandstones of Lower Carboniferous (Mississippian) age. The metasediments occur as a flysch sequence which trends north to north-north-east (UTM) for at least 20 km. Shale is the dominant rock type. Sandstone units are up to several metres thick but are generally less than 30 cm thick, with the thicker sandstone units being restricted to the western part of the project area.
Subsequent to deposition the sediments underwent substantial ductile and brittle deformation during the Variscan orogeny. Resulting bedding is commonly moderate to steeply dipping to WNW. Frequent metre-scale tight parasitic folds are observed over the project area, mostly gently plunging NNE, moderately inclined WNW and ESE-verging.
The regional trend of the strike of the host rocks is north to north-north-east. The Achmmach hill which trends 70 degrees east of north translates a change in strike explained by the occurrence of resistant tourmaline and silica-bearing structures.
The metasediments have been intruded by sub-volcanic felsic and mafic igneous rocks. The Palaeozoic sequence has been intruded by Hercynian (Upper Carboniferous-Permian) granite, which outcrops about five kilometres to the west of Achmmach. The host rocks have been overprinted by fine grained black tourmaline over a strike length of at least 1.6 km and a plan width of 200 m to 500 m. This tourmaline alteration corridor is a distinctive feature in the area mapped from the Bou-El-Jaj prospect to the south west corner of PE2912 trending NNE and across PE2912 trending ENE.
The east-west striking Sidi Addi Fault is the main structural feature at Achmmach and occurs in the northern part of the deposit.
Tin mineralisation at Achmmach occurs as cassiterite in quartz-cassiterite veinlets and stringers, and as disseminations. The veinlets and stringers are commonly narrow, up to a few millimetres thick. Thicknesses up to a few centimetres occur locally. The host rocks were altered by black tourmaline and white quartz before the introduction of cassiterite as stringers and veinlets. Tin presents as disseminations in black tourmaline and as infill to some breccias.
Taylor (2009) suggested a paragenesis, the stages of which most relevant to the tin mineralisation are:
Kasbah geologists have noted a general relationship between tin grades and the mode of occurrence of cassiterite as outlined in Table 3 1.
Table 3 1: Cassiterite Occurrence at Achmmach
The Achmmach Tin Project comprises mineralised envelopes or lodes, which are known over a strike length exceeding 1.6 km. Close-spaced drilling has enable the identification of east-west striking sub-vertical tourmaline envelopes described as “feeders” and gently to steeply north dipping “branches”. The tourmaline envelopes have been defined by drilling over a vertical interval of approximately 600 m. The envelopes range from a few metres to over 30 m thick. The mineralised envelopes appear to be relatively continuous in plan, reflecting the continuity of the tourmaline alteration mapped at the surface.
The occurrence and spatial distribution of the cassiterite veinlets in the mineralised envelopes dictates the distribution of tin which needs to be taken into account during grade interpolation. In summary, there are several features of the tin mineralisation which are important to the resource estimate:
In 2002, BRPM (subsequently ONHYM) evaluated a resource for Achmmach by completing a programme of 29 diamond drill holes and bulk sampling from an underground exploration adit on the 890mRL level.
Using this data, ONHYM produced an unclassified resource estimate of 9.57 Mt containing 1.09% Sn at a cut-off grade of 0.50%. This estimate does not comply with the JORC guidelines and therefore was not classified as Mineral Resources under this code.
As a result, additional resource definition work was undertaken by Kasbah with the aim of defining a JORC-compliant resources.
The lastest JORC 2012 compliant resource upgrade was revised by QG in November 2014. It is based on the completion of 270 diamond drill holes totalling 102,905 m. The resource estimate is based on a cut-off grade of 0.50% Sn. Table 3 2 shows the breakdown of the prevailing Mineral Resource at Achmmach.
The classification of the entire resource of the Meknès Trend falls within Measured and Indicated categories.
Table 3 2: Meknès Trend Mineral Resource Estimate
(Estimated as at 24 November 2014)
The Achmmach Project is covered by two exploitation permits (PE 2912 and PE 193172), covering a total area of 32 km². Under the terms of the agreement with ONHYM, Kasbah acquired 100% of the Achmmach Project and its permits during 2012, after having completed a Scoping Study on the project in late 2010.
Atlas Tin SAS (ATS) as the Moroccan Joint Venture company now holds 100% of the permits.
The Achmmach deposit is located in the Paleozoic Central Massif of the Western Meseta Domain, which itself is part of the larger Variscan (Hercynian) Orogenic belt. This Hercynian belt is developed around the 2 Ga-old continental nucleus of the West African Craton through repeated oceanic closures and collisional orogenic events from 460-420 Ma (Caledonian) to 360-300 Ma (Hercynian). The Atlas-Meseta domain is strongly deformed, weakly metamorphosed and intruded by varied granite massifs.
Figure 3 1 illustrates the Variscan orogenic belt.
Figure 3 1: Reconstruction of the Variscan Orogenic Belt (380-260 Ma) with Locations of Major Tin Deposits
The Palaeozoic terranes of the Meseta Domain are widely covered by Mesozoic-Cenozoic formations and as a result, are exposed as isolated massifs. The Western Meseta is composed from north to south of the Central, Rehamna and Jbilet massifs. It is further subdivided into the Western Central Meseta and Eastern Central Meseta by the Smaala-Oulmès Fault Zone and the NE-trending Moulay Bou- Azza Fault.
The Achmmach Deposit is located about 2 km east of the Moulay Bou Azza fault in the Eastern Central Meseta as shown in Figure 3 2.
Figure 3 2: Moroccan Geologic Domains
Three main Hercynian granites outcrop within the Central Massif; the Zaer Granite in the west, the Oulmès granite in the central-east, and the Ment Granite in the east. The Oulmès Granite hosts the El Karit Tin Deposit where tin mineralisation occurs as cassiterite in small lensoid quartz veins over an area nearly 5 km long and 250-500 m wide. Tin-tungsten mineralisation is also associated with the Zaer Granite and the Ment Granite.
Early regional mapping (Termier, 1936) identified a 15 km x 8 km contact metamorphic aureole covering an area extending from El Hammam to Achmmach, suggesting the presence of a large buried granite. However, no large intrusives outcrop within the Achmmach deposit area, only a clustered occurrence of small monzogranite outcrops in the Oued Beht (River), 5 km west of Achmmach with associated tin-tungsten bearing skarns.
The Achmmach deposit is located within the turbiditic (flysch) deposits of the Namurian Fourhal Formation. The host rocks continue to the south west as shown in Figure 3 3.
Figure 3 3: Achmmach Regional Geology (and Kasbah / ATS Permits)
ACHMMACH DEPOSIT GEOLOGY
The Fourhal Formation comprises a series of folded, sheared and weakly metamorphosed shales (pelites) and sandstones (psammites) of Lower Carboniferous (Visean-Serpukhovian) age. These meta-sediments are interpreted as a series of turbidites deposited in the Fourhal Basin. Generally found in outcrop and drill core, shales, siltstones and sandstones are interbedded on centimetre to decimetre scale as illustrated in Figure 3 4.
Figure 3 4: Typical Interbedded Sandstones and Shales at Achmmach
The meta-sediments have been intruded by number of sills and dykes with metric to first decametric width. Their composition varies from basic - intermediate (dolerite, gabbro and microdiorite) to felsic (monzogranite, microgranite and rhyolite). The strike continuity of the intrusives varies from tens of metres to more than a kilometre. The majority of the intrusives are interpreted as being pre-mineralisation as commonly they are tourmaline-altered and carry tin mineralisation. The mafic types are clearly more abundant in the Eastern segments of the deposit, while in the Central and Western parts one felsic and one mafic intrusive could be consistently traced. The felsic intrusive (monzogranite) is of particular interest as it commonly defines the hangingwall of high-grade mineralisation in this area.
The rocks at Achmmach have experienced substantial repeated deformation during the Variscan Orogeny period that led to the closure of the Fourhal basin, folding and faulting of the deposited sediments and the intrusion of various suites of igneous rocks.
Bedding in the area is normally moderate to steeply dipping to WNW with some local variations. Numerous metre-scale tight parasitic folds are identified. Vergence is generally to ESE while fold axes are gently plunging NNE. Asymmetries of the limbs of the small folds indicate that Achmmach is probably located on the western limb of a major anticline (Compston, 2011). Commonly the folds hinges are sheared and thrusted to the ESE along the axial planar cleavages. Syntectonic milky quartz veins are abundant in these zones. Ubiquitous across the deposit is a subvertical E-W to WSW striking spaced fracture cleavage.
It is argued that this development is related to a transition to transpressional deformation conditions. These structures have a major control on the distribution of the tourmaline alteration and subsequently the tin and sulphide mineralisation.
Late brittle faulting has limited extent at Achmmach. It is restricted basically to the ENE-striking, North dipping Sidi Addi normal/dextral wrench fault and several shorter range cataclastite zones. These have experienced only minor displacement, as no major off-set of the principal structures has been recorded.
The rocks at Achmmach bear signs of extensive modification by epigenetic hydrothermal fluids that are believed to be related to deeper granitic intrusions. The large volume of the hydrothermally altered rocks is indicative of a large paleo-hydrothermal fluid system. These fluids are thought to have intermittently released into the higher crust with evolving chemical and physical properties responsible for the alteration halo and subsequent mineralisation. Two main types of alteration are distinguished at Achmmach:
Figure 3 5 below illustrates these alteration types.
This alteration is also strongly structurally controlled, developing along the steep E-W fracture cleavage which also preferentially invades shear zones, fold hinges or advances along bedding, and locally forms extensive hydraulic breccias. The tourmaline alteration acts as a host to the main quartz cassiterite veins and breccias which contain the bulk of the tin in the deposit. In general the absence of tourmaline alteration suggests absence of significant tin. However, the presence of tourmaline is no guarantee of tin mineralisation.
Figure 3 5: General Geology of the Achmmach Deposit and Alteration Zones
Two sub-types of tourmaline alteration have been identified during microscopic studies but are not easily distinguishable with the naked eye:
Similar to many other tin provinces in the world, the mineralisation stage at Achmmach is a natural part of the evolution of the hydrothermal system forming around specific fractionated granitoid plutons. Taylor (2008, 2009) summarized the progressive changes in the mineral paragenesis from the earliest to the latest stages of development of the system as shown in Table 3 3 below.
The stages that are most relevant to the formation of the deposit are:
Being an event that carries the tin-chloride complexes that deposit the main volume of cassiterite in suitable structures.
Table 3 3: Achmmach Alteration/Mineralisation Paragenesis Modified from Taylor 2008, 2009
The mineralisation is developed predominantly within the intense tourmaline-silica altered meta-sediments commonly referred to as “lodes”. It occurs mostly as veinlets, and cm wide veins. Disseminations within the acicular Tourmaline II or the porous sandstone beds are locally important.
High grade ore shoots are normally associated with dense fracture / stockwork arrays, bigger and high frequency sheeted veins reaching up to few cm thickness, and also hydraulic breccias as shown in Figure 3 7.
Figure 3 6: Black Tourmaline II –Quartz Alteration and Milky Quartz I
Figure 3-7: Fine grained cassiterite (brownish) as vein infill and dissemination along the edges with late stage cross cutting carbonate (whitish) veins
The bulk of tin mineralisation occurs as cassiterite (SnO2 – S.G. 6.80-7.10, 78.6% Sn). Although stannite (Cu2FeSnS4) occurs in some veins, it is not a significant mineral in the deposit. Cassiterite is usually relatively fine grained (50 µm to 120 µm) with a brownish-grey colour. It is relatively pure in composition and does not carry significant trace elements (e.g. In, Ga, Ta or Nb).
Table 3-4 describes the mode of occurrence of cassiterite in terms of grade.
At Achmmach it appears that the main stages of mineralisation are superimposed on one another (telescoping effect) and as such no obvious zonation is apparent. Each stage exhibits a vertical extent of several hundred metres, and any zonal effects will only become obvious at the upper and lower extremities of the system.
Table 3-4: Tin Grades and Modes of Occurrence of Cassiterite at Meknès Trend.
By Kasbah Resources
In 2005, Kasbah commenced the acquisition process of the Achmmach Tin Project from ONHYM. At first, the BRPM data package was reprocessed by Carras which led to a JORC compliant inferred resource of 2 Mt @ 1% Sn at a 0.6% Sn cut-off. Since then Kasbah, has worked on the licence alternating between surface works and drilling campaigns.
Completed surface work includes:
Since commencing the first drilling campaign in 2007, Kasbah has employed four contractors to conduct diamond drilling over PE2912. Diamond core was orientated whenever possible using Eazymark or Reflex ACT tools.
In parallel with the drilling programs, various consultants have been commissioned to carry out petrological and structural analysis on core. Consultants and studies were as follows:
Resource estimation consultants were commissioned several times between 2007 and 2013 as described in the following.
Mineral Resouce Estimates
Mining One Pty Ltd
In Q1 2012 Kasbah engaged Mining One to prepare a third JORC compliant resource estimate. This estimate was based on diamond drilling completed from late 2010 through early 2012, which mostly consisted in covering the Gap Zone by 80 m infill sections.
The geological interpretation used as the framework for the Mining One resource estimate was completed by Kasbah’s geologists. The envelopes shown in the middle right of Figure 3 8 capture tourmaline alteration associated with tin grade. Alteration intensity was derived directly from logging records. The mineralised envelopes generally dip moderately to steeply north with an average dip/dip direction of -50/350. The mineralised envelopes appear to be relatively continuous in plan, reflecting the continuity of the tourmaline alteration mapped at the surface (Figure 3 5). In cross-section, the mineralised envelopes have been referred to as “stacked lodes” and each envelope is separated from, and off-set to the south relative to the lode above it.
Mining One obtained the following JORC compliant Resource estimate as detailed in Table 3-6 of:
Figure 3 8: Drilling and Geological Model Evolution of the Meknès Trend from 2002 to 2013/09 and Successive Resource Estimations
The two most recent resource estimates from QG relate to the current geological model and are described in the following.
Current Geological Model
With the infill drilling at 40 m spacing over the Gap Zone and the Meknès Eastern Zone, together with the subsequent 20 m-spaced infill drilling of 240 m of strike length from 2390 mE to 2630 mE, it became apparent that north-dipping oblique tourmaline envelopes coexist with sub vertical east west striking envelopes.
In order to create tourmaline alteration zones, Kasbah used potassium (K) as a proxy as it is progressively depleted as the intensity of tourmaline alteration increases (Barabino, internal report, 2011). As a result, tourmaline alteration envelopes associated with grade used for the latest resource estimates in 2013 are less dependent on logging data that can occasionally be subjective.
Given the above, both 2013 resource estimates interpret the Meknès Trend as being defined by several ENE-WSW striking sub-vertical mineralised structures. These sub-vertical structures described as “feeders” are the presumed conduits for the granite-emanated fluids which carry tin mineralisation. As these fluids reached higher levels, they produced tourmaline alteration haloes within the deposit and deposited tin mineralisation in favourable trap sites that pervade up and down dip from the feeders described as “branches”.
Figure 3-9 highlights examples of trap sites in the context of the current geological model.
Figure 3 9: 3D Diagram Looking West of the Achmmach Geological Model Sliced at 2450m E (local grid).
Several unknowns about the geology at Achmmach remain: