Project
upgrading the small two million tonnes
(Mt) JORC-compliant resource by way
of additional diamond drilling, then
advancing the project through scoping
study, pre-feasibility study, DFS and
ultimately, full project development.
•
The road to SSO
During this process, Toyota Tsusho
Corporation (TTC) and Nittetsu Mining
Company (NMC) of Japan became
project-level strategic partners (TTC
acquiring a 20% interest and NMC a 5%
interest in the project).
By 2015, KAS had completed in excess of
130 000m of diamond drilling into the main
Mèknes Trend at Achmmach, expanding
the JORC resource to 14.9 million tonnes
(Mt) at 0.85% tin (Sn) for about 127 300t
of contained tin. It also announced a JORC
Reserve for Achmmach of 9.2Mt at 0.77%
Sn (for approximately 71 300t of contained
tin) and completed an enhanced definitive
feasibility study (EDFS). The EDFS
integrated the high-grade Western Zone
(WZ) target (from the largely untested Sidi
Addi Trend) into the full one million tonne
per annum (Mtpa) Mèknes mine design.
Integrating the WZ extended the mine
life with almost 10 years, reduced pre-
production capital costs, and significantly
reduced C3 cash production costs to
USD13 296/t of tin-in-concentrate. In
2016, KAS revised the scale and the
scope of Achmmach in response to weak
commodity pricing, instead looking at
a more modest operation, known as
the Small Start Option (SSO), which
would treat up to 750 000tpa of tin. KAS
subsequently released a DFS that produced
further substantial reductions in capex to
USD61.7-million and C3 operating cost of
USD13 811/t tin in concentrate, based on
an ore reserve of 6.6Mt at 0.85% Sn.
In 2017, KAS announced the results of an
independent technical review of the SSO
by AMC, with work now under way on
implementing the recommendations made,
the results of which will be released in a
revised DFS in 2018.
Geology: an overview
The following key points apply to the
Achmmach deposit mineralisation:
• Tin mineralisation comprises fine-
30 AFRICAN MINING MARCH - APRIL 2019
•
•
grained cassiterite with associated minor
sulphide minerals in a tourmalinised
sandstone/siltstone shale host;
A robust and unbiased technique for
tourmaline mapping, based on the
potassium content as a proxy, was
established and used for the latest
geological interpretations in 2013;
It has become apparent from tightly
spaced drilling interpretations
that subvertical east–west striking
tourmaline zones co-exist with
oblique north-dipping ones;
The significant increase in drill hole
data has enabled the classification
of the entire Meknès Trend as a
measured and indicated resource,
translating into high confidence
in geometry and continuity of the
mineralisation.
The Achmmach tin mineralisation is an
epigenetic vein-stockwork-breccia type
deposit associated with a strongly boron-
enriched paleo-hydrothermal system. It is
interpreted as being hosted by two cross-
cutting swarms of tourmaline-altered zones;
a series of east–west striking subvertical
zones described as ‘feeders’, and a stacked
series of oblique gently to steeply north-
dipping ‘branches’.
The 1.6km strike extent of the
mineralisation system is entirely hosted by
sequences of folded and metamorphosed
shales and sandstones. The lodes form
a 300m-wide array across strike, with
individual lode structures ranging from 1m
up to 30m wide. Tin mineralisation occurs
primarily as breccia infill and quartz-
cassiterite veins and has been defined in
diamond drill holes to a vertical depth of
about 600m below natural surface. The
deposit is open at depth and along strike.
Local geology
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 20km. Shale is the dominant rock
type. Sandstone units are up to several
metres thick but are generally less than
30cm 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
subvolcanic 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 1.6km and a plan width
of 200–500m. 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.
Project geology
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. Sources
suggested a paragenesis, the stages
of which most relevant to the tin
mineralisation are:
• Tourmaline II and Quartz II occur
together, and rock containing moderate
to strong Tourmaline II mineralisation
is host to the tin mineralisation; and
• Quartz-cassiterite ± arsenopyrite,
pyrite and chlorite mineralisation
contains the tin.
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