The Motagua River lies adjacent to and south of the Sierra de Chuacùs Mountains. The Motagua is a Medium sized river that flows to the east. The study sites have been mapped as being characterized predominately by two formations composed of ultrabasic rocks of unknown age; mainly serpentines and also undivided paleozoic metamorphic rocks; phylllites, chlorite and garnet schists, quarz-mica-feldespar schists and marbles and migmatites. Site reconnaissance of the study sites revealed mostly serpentine bedrock with many of the aforementioned metamofphic rocks present in the stream gravels which conforms to the regional mapping of the area.
Intrusions of quartz were observed in several places throughout the country rock and may be the source of the gold placers. Metamorphic rocks of this nature have been known to host gold values of varying degrees. Lower grade deposits can contribute significantly over time to the gold deposits retained in the stream gravels. Information received from local people suggest there are areas where small amounts of gold that are visible to the naked eye are present in a quartz vein.
Exposed serpentine bedrock and associated stream gravels were observed throughout the Motagua River study area. Grain sizes of the stream gravels range from clay size to very large boulders. The degree of cementation of the stream gravels will not be known until further exploration are done.