The Monte do Carmo project is 100% owned by Hochschild Mining PLC, held through its Brazilian subsidiary Amarillo Mineração Do Brasil Ltda., following the project’s acquisition from Cerrado Gold in November 2024.
- subscription is required.
Summary:
The principal target of interest for Cerrado Gold is the Serra Alta Deposit which appears to have the best potential for the development of significant tonnage. As such, the remainder of this report will concentrate on Serra Alta, with only brief descriptions of other target areas.
Deposit Types
Two main deposit types (+ subtypes) are currently recognized at the MDC Project:
- Reduced intrusion-related gold (± coeval sheeted veins);
- Orogenic/lode gold (regardless of host-rock type).
Reduced intrusion-related gold systems (RIRGS) represent a newer genetic model relative to orogenic gold systems, having only been recognized by researchers since the 1990s to early 2000s as analytical capabilities improved. They can be difficult to distinguish from their orogenic counterparts due to shared/overlapping characteristics and often similar geological settings (Hart and Goldfarb, 2005; Lafrance, 2019). The problem is that intrusions may be emplaced in large deformation zones, and the associated (± sheeted) vein sets may be later sheared and mistaken for orogenic vein systems (Lafrance, 2019).
Serra Alta Mineralization
The Serra Alta deposit is interpreted as an intrusion-related gold system, with mineralization associated with hydrothermally altered and locally veined granitic rocks. Abundant mineralized shoots are clearly controlled by varying densities of vein and veinlet swarms that are weakly enriched in sulphides (pyrite, galena, sphalerite and chalcopyrite). The deposit currently comprises 8 main zones that span approximately 2 km of strike length (oriented 190–195o ) with an overall width of ~600 m, and dip moderately to steeply (55–75o ) to the west-northwest with a vertical extent on the order of 200 m. In general, individual mineralized lenses (i.e., shoots) range from approximately 5 m to greater than 30 m in width.
Sheeted vein sets mostly follow the overall deposit trend; however, the presence of multiple mineralized vein orientations indicates a more complex system that evolved over several mineralization and deformation events, as evidenced by the structural history of the area. There are two main northeast-trending (~N30oE) faults that flank the mineralization at Serra Alta, with a series of smaller east-west (± 30o ) faults that delimit the deposit into discrete structural blocks; as such, each zone requires individual modelling and estimation to respect these constraining features. The lateral extent of the sheeted vein swarms is wider towards the intrusive contact between the main granitic host rocks and overlying felsic volcanics. This intrusive contact is interpreted to act as a cap throughout much of the deposit.
Field observations from historical small-scale mining conducted by MSM at Serra Alta (North and South Blocks) support the notion of an intrusion-related genetic model for the gold mineralization hosted in the cupola portion of the Monte do Carmo granite. Mineralization occurs within a system of veins and veinlets commonly associated with zones of hydrothermal alteration (typically phyllicpropylitic in nature). This alteration is commonly characterized by the presence of quartz, epidote, chlorite, tourmaline and sulphides (pyrite, arsenopyrite, galena, sphalerite and chalcopyrite). The sulphide content in mineralized zones is generally estimated on the order of 0.5 to 1.0% by volume.
Though the granite appears host to a complex system of vein sets with multiple orientations, historical field mapping and drilling identified two main intersecting trends (NE-SW and NW-SE), which occur in most areas of the deposit. The veins/veinlets in the NE-SW-oriented set are generally mm- to cm-scale, and appear to truncate those of the older system. This veining is predominantly composed of moderately fractured, medium to coarse-grained milky quartz, with rare aggregates of white mica + chlorite + carbonate. Vein selvages and internal zones of expansion are often filled by sulphide minerals and free gold.
Occasionally, multiple expansion and filling phases are identified in the NW-SE system, cutting the NE-SW milky quartz vein system. This may represent a late stage of dilation recorded in the granite dome. It is filled with aggregates of chlorite + white mica + carbonate ± pyrite as veinlets.
The presence of different phases of dilation is interpreted to be indicative of successive episodes of reopening and filling of cracks, which are independent, but can effectively occur simultaneously or in short succession. This characteristic favours a model based on successive fracture events in the cupola, the product of increased pressure of confined hydrothermal fluids (Jensen & Bateman, 1981; Guha et al., 1983; Foxford et al., 2000).