- LOCATION
The Dousseoussou marble quarry is located approximately 610 km from Libreville by road and approximately 17 km from the town of Tchibanga, provincial capital of the Nyanga province, on the Tchibanga-Mayumba road.
The Latitude/Longitude coordinates of the quarry are: 03°02.189 S and 010°52.744 E.
Figure 1: Location and situation map
- GEOLOGICAL CONTEXT
The Dousse Oussou area belongs to the folded and metamorphosed western flank of the Nyanga syncline, consisting of the Schisto-Calcareous Group of Neoproterozoic age.
The Dousse Oussou marble zone corresponds to a unit of dolomites and limestones of the lower part (SC1) of the Schisto-Calcareous Group, undeformed and unmetamorphosed on the eastern edge of the basin. The latter is affected on the western flank of the basin by strong thermal metamorphism, related to the emplacement of Pan-African intrusive plutons. This episode led to marmorisation (transformation of limestones and dolomites into marble).
The colors of the marbles vary from white to gray and present a great variability of facies.
Figure 2: Synthetic geological map of Gabon showing the location of the marble in the Nyanga syncline on the right and the location of the SEM area of interest.
- PREVIOUS WORK
During the first exploitation of the Dousse Oussou marble quarry in the 1970s, notably for the construction of the presidential palace and the 12 March congressional palace (now the Cité de la Démocratie), a study dated 1975 was carried out by the Gabonese geological service.
This study included a mapping of the outcrops and the realization of soundings:
- Observation of outcrops
No less than 45 different outcrops have been identified. The observation of the outcrops allowed to highlight the presence of 3 main types of marbles:
- A grey marble
- A white veined marble
- A whitish to beige marble, with brown-pinkish streaks.
- The realization of surveys in 1974/1975
23 core holes drilled in various points near the exploitation area reveal the presence of the following marbles at varying depths with some of optimal quality for exploitation:
- Bardiglietto Venato
- Bardiglio Venato
- Bianco Venato
- Bardiglio
- Bianco colorato Marrone Rosso
- Bianco Rosato Sul Marrone
All of the above marbles are recommended for both interior and exterior use and their equivalents are generally of Italian origin.
More recent work was carried out in 2013. This work consisted of taking samples and performing porosity tests and bulk density determination.
- Marble tests and analysis
In 2013, marble samples recovered from the area of the former quarry were analyzed at a laboratory in France to determine the porosity of the marble as well as its density. The results obtained are satisfactory presented below:
Figure 3: Table of test results
- ESTIMATED RESOURCES
Despite the fact that the Dousse Oussou quarry was exploited in the 1970s, no reserve estimation data is available.
However, given the extent of the area in which the geological formation containing the marble extends, it is possible to envisage potential geological resources of the order of several million tons in the entire region.
A more detailed study with the execution of core drilling is necessary to make an assessment of the exploitable reserves. In 2015, SEM planned a program of 30 drill holes to determine and certify the reserves in the area of interest shown in Figure 2.
- CONCLUSION
In view of the geology, the marble resources in the Dousse Oussou area could be in the region of several million tons. The mechanical characteristics of the marble are perfectly compatible with international standards. However, in view of the variability of the deposit, a study to determine the reserves by type of marble is necessary.
