Summary:
Deposit type and geology
The mineralisation at the MGM is collectively hosted by granodiorite stock and feldspar porphyries. These lithologies are host to a multitude of narrow, sub-parallel mineralised shear zones, which form an imbricate thrust shear zone system (GFM 2018).
To date more than 15 sub-parallel shear zones have been identified. These shear zones strike east-west and dip to the north at approximately 10 to 50° degrees. Slickenside lineations plunging 50° to the northeast are evident throughout the mine. From north to south, mining has exposed the following mineralised shear zones (GFM 2018):
— Flowing Bowl.
— S.O.S.
— Bucks.
— Bojum/Wimbledon.
— Connaught.
— Nucleus.
— Birthday.
— Carnbrae.
— Shear zones are generally separated by unsheared zones (lithons) of ± 30 m in width.
These shear zones splay and link in an anastomosing pattern, along strike and down-dip, as demonstrated by the Nucleus Reef on lower levels. The east-west striking mineralised shear zones show dominantly reverse movement, with a component of sinistral oblique slip.
More recently, it has been noted that mineralised shear zones dip to the south at 5 to 25°. The north dipping mineralised shear zones are either displaced, or apparently terminated against the south dipping mineralised shear zones, suggesting that the latter are later features (GFM 2018).
The only major faults that displace the mineralised shear zones are strike-slip faults, one of which terminates the Nucleus and Birthday reefs at their eastern extremities. This fault has a sinistral reverse sense of displacement, indicating a strong likelihood that extensions to the Nucleus, and Birthday reefs may be present east of the fault (GFM 2018).
Mineralisation
The mineralisation at the MGM is collectively hosted by granodiorite stock, concentrated around the northeastern tip and extending eastwards into the feldspar porphyries, both with a similar style of mineralisation (GFM 2018).
Mineralisation varies somewhat with the type of country rock through which the mineralised shears zones pass. In most cases, gold is strongly associated with sulphide mineralisation and only to a limited degree with quartz veins. Typical quartz-pyrite mineralisation widths vary from less than 1 centimetre (cm) to approximately 20 cm, in shear zones of widths of ± 1 m (GFM 2018).
In the granodiorite, the principal sulphide is pyrite, which occurs in white to grey quartz. Scheelite, pyrrhotite and arsenopyrite also occur. Two ages of pyrite mineralisation are apparent, the oldest being a coarse crystalline pyrite, which is heavily fractured and intruded by younger quartz and pyrite. The younger pyrite is fine-grained or massive and contains myriads of quartz inclusions. Wall rock alteration of the east-west striking mineralised shear zones in the granodiorite is generally minor. Where shear zone splaying or anastomosing occurs however, the granodiorite is brecciated and saussuritised to a dark grey colour (GFM 2018).
In the porphyries, pyrrhotite becomes more abundant than pyrite and quartz is less common. Where sheared and mineralised, the feldspar porphyry is bleached and altered to a brownish colour (GFM 2018).
It is thought that the ore zones were formed by pulsating hydrothermal solutions, migrating along structurally controlled channels resulting from reverse dextral shearing in an imbricate thrust shear zone system (duplex) [GFM 2018].
Commodity Production
Mazowe mine has been on Care and Maintenance since 31 December 2018, with some small-scale processing of artisanal miner ore still conducted at Mazowe, formerly under the supervision of a business administrator.
| Commodity | Units | 2023 | 2022 | 2021 | 2018 | 2017 | 2016 | 2015 |
All production numbers are expressed as metal in doré.