The Mengapur Project is located in the Malaysian state of Pahang and 100% owned by Monument Mengapur Sdn Bhd (MMSB) in Malaysia, which in turn holds tenements through two wholly-owned subsidiaries, Cermat Aman Sdn Bhd (CASB) and Star Destiny Sdn Bhd (SDSB).
Mengapur (CASB) Mine was acquired by Fortress Minerals Ltd. in April 2021 through the Fortress Minerals Ltd.’s acquisition of Monument Mengapur Sdn. Bhd., the holding company of Cermat Aman Sdn. Bhd. ("CASB”) and Star Destiny Sdn. Bhd. Following the acquisition, the name ‘Monument Mengapur Sdn. Bhd.’ was changed to ‘Fortress Mengapur Sdn. Bhd.’.
Summary:
Mengapur geology is dominated by sedimentary rocks that have been intruded by at least one dyke complex. The dyke icomplex outcrops in the centre of the deposit and forms a steep resistant ridge that is referred to as Bukit Botak. The sedimentary rocks adjacent to the Bukit Botak intrusion complex and other nearby buried intrusions are altered to skarn.
The Mengapur limestones are typically massive and locally fossiliferous and/or interbedded and can be separated into two distinct facies: a calcareous facies and an argillaceous facies. The younger calcareous facies consists of dark grey carbonaceous limestone locally interbedded with calcareous shale. The argillaceous facies consists of calcareous shale, graphitic slate, quartz-sericite phyllite, schist, quartzite, and minor interbeds of andesitic, dacitic, and rhyolitic tuff. The sedimentary rocks generally strike north-northeast and dip steeply (45° to 85°) to the east-southeast.
The dyke complex is dominated by adamellite (quartz monzonite) with lesser amounts of rhyolite, rhyolitic tuff and rhyolite breccia and is approximately 800 m in diameter in surface exposures and has been encountered in historical drilling up to 600 m below the surface. The intrusion complex contains moderately to locally very steep contacts with the adjacent sedimentary rocks and reaches up to 900 m in width at depth. The intrusive rocks appear to intrude sub-parallel along the original sedimentary rock bedding as they generally strike approximately 60° to 65° at the surface and generally dip 55° to 65° to the eastsoutheast forming large dyke-like bodies.
The structure in the area is dominated by north-south and northwest-southeast trending high-angled faults and folding. The Bujit Botak Intrusive Complex intruded the Mengapur limestone sequences along the western limb of a synclinal fold. Oriented core drilling identfied two dominant fault orientations at Mengapur: a set striking 10° to 30° and a second set striking 270° to 315°.
Weathering of the skarns is locally very deep at the margins of the intrusive complex where the oxide zone can locally reach up to 300 m in depth. The oxidation is deepest on the northern and south-western flanks of the intrusive complex. In the south-eastern part of the mineralisation, oxidation reaches up to 120 m deep.
Hydrothermal alteration at Mengapur is centred on the Bukit Botak intrusive complex with some hornfels and mostly mineralised skarn occurring in the adjacent sedimentary rocks at the intrusive-sedimentary rock contact zone. The skarn alteration extends outward into the sedimentary rocks approximately 300 m to 650 m laterally from the contact and has been intercepted in drillholes up to 750 m below the surface. The skarn alteration halo around the Bukit Botak intrusion complex dips steeply to the southeast.
The Mengapur deposit contains Cu-Au(±Ag±Fe) mineralisation hosted predominantly by pyroxene-rich and garnet-rich exoskarn that occurs adjacent to the felsic intrusions. The known Cu-Au mineralisation extends over a 1.2 km x 1.5 km area in a concentric geometry haloing the contact of the main Butik Botak intrusion complex and extends up to 630 m below surface.
The Mengapur deposit hosts three types of mineralisation:
- Sulphide (hypogene) Cu-Au(±Ag±Fe) mineralisation;
- Transitional mineralisation that contains mixed oxide and sulphide mineralisation near the oxidesulphide redox contact;
- Near-surface oxide Cu-Au(±Ag±Fe) mineralisation.
Both the garnet-rich and pyroxene-rich skarn varieties contain low to locally high amounts of sulphide and/or iron-oxide minerals. The most dominant sulphide mineral in the skarn is pyrrhotite followed by lesser amounts of pyrite, chalcopyrite, arsenopyrite and molybdenite. Accessory sulphide minerals in sulphide mineralisation includes: molybdenite, galena, sphalerite, marcasite, chalcocite, covellite, cuprite, native copper, native bismuth, boulangerite, bouronite, tetrahedrite, scheelite, freibergite, pyrargyrite, cassiterite, kesterite, anglesite and native gold. Pyrrhotite occurs as either massive zones or disseminated within the skarn.
Chalcopyrite is the dominant copper mineral in the mineralised sulphide skarn and occurs as fine disseminated grains and locally within late quartz-rich veins. The 0.1% Cu mineralised envelope in the sulphide zone generally forms a wide zone that extends up into the adjacent transitional and oxide zones. Only rare bornite has been logged in some drillholes.
Planar quartz-rich veins up to 2 m in width locally cut the skarn assemblages as sheeted veins at similar orientations and contain various amounts of the following sulphide minerals in approximate order of abundance: pyrite, chalcopyrite, arsenopyrite, molybdenite, pyrrhotite, galena, sphalerite, tetrahedrite and native bismuth. These veins are visible in rock outcrops in the Malaco open pit located south of the intrusion complex where the quartz veins are gently to moderately dipping to the east and spaced approximately 0.5 m to 2 m apart. Accessory minerals in the quartz veins may include calcite, sericite, and siderite. Monument indicated that elevated gold assays are often associated with these veins.
Transitional mineralisation, which typically hosts variable sulphur grades and locally high Cu grades (>0.3% Cu), occurs below the base of the oxidised zone and above the sulphide mineralisation in the bedrock skarn.
Similar to the sulphide mineralisation, the transitional mineralisation haloes the circular contact of the Bukit Botak intrusion complex with the skarn but tends to be poddy and discontinuous. Transitional mineralisation is generally fairly narrow, ranging from a few metres up to 30–50 m, but can locally range up to 90 m thick where higher fracture densities and/or faults are present.
Oxide Cu-Au-Ag-magnetite mineralisation is hosted in soil, weathered skarn, gossan and locally in other weathered rocks based on assays from Monument exploration drillholes. The weathered skarn may be strongly weathered to depths up to 150 m below surface.