Geochemical Studies of Springs in a Volcanic Area, Case of Virunga and Kahuzi Bienga, DRC

Proceedings, 8th African Rift Geothermal Conference Nairobi, Kenya: 2 – 8 November 2020

Geochemical Studies of Springs in a volcanic area, Case of Virunga and Kahuzi Bienga, DRC

1Kambale Kavyavu W., 2Makabu Kayembe G.

1 Assistant /Université de Goma, Democratic Republic of the Congo, Goma Town, +243999154269,

2Professor / Université de Lubumbashi

Keywords: Kivu-Volcano-Energy-Geochemistry-Geology-Structural

ABSTRACT The best practice in making geothermal development decisions is to integrate all the sciences to develop a comprehensive model, provide simulations on how to make high-value geothermal decisions to improve well targeting using time data, William B . Cumming 2018, Geothermal data integration and modeling helps in enhancing precise good targeting, Data sets from resources similar to the eastern and western branches are separately integrated using on key criteria when making decisions for each unique resource to help understand , how to develop conceptual models for target wells and assess resource capacity of volcano hosted system and a deep circulation system. A review of geologic map data, developing conceptual models, and targeting wells will precede drilling, Geochemistry of springs will guide the understanding of a reservoir and the future geophysical feature in the future will show the stratigraphy, of the bottom and top of the reservoir. Surface temperatures range from 30ºC to 100ºC and the springs are neutral to alkaline (pH 6,2 8,9). Chemical analysis of all samples shows strikingly high bicarbonate content relative to the common major anions in hot springs. Their calculated reservoirs temperature ranges from 150 to 270ºC in North Kivu geothermal areas and ranges from 277 to 369ºC in South Kivu. Rwindi hot springs in Virunga National Park are mature while others are immatures water and are peripheral bicarbonate waters.

1. Introduction The main role of geochemical surveys in all geothermal exploration phases is to obtain information on the origin of the geothermal fluid and to understand the subsurface flow directions using subsurface characteristics such as temperatures and chemical concentrations analysis. The Democratic Republic of Congo geothermal reservoirs in the rift zone is only manifested by the presence of thermal springs. Geothermal exploration reveals hidden reservoirs and locates geothermal sites in an economically feasible way. Many East African countries are looking at their indigenous geothermal resources as a source of electricity and heat, to date the main focus has been on power production from high- temperature geothermal resources which is understandable, considering the shortage of electricity in the region and the promising availability of resources. the region also has low- temperature geothermal resources, the potential of which has not been well evaluated limiting utilization. This does not only apply to the East part of East African Rift, where the potential for electricity is high, but even more to its West part, which is not endowed the same type and

Kambale & Makabu the number of volcanic systems providing a heat source from historically high- temperature geothermal systems ( Pre-ARGeo C7, 2018) except for Kenya, all African ARGeo’s members countries are exploring geothermal reservoir including DRC which is the focus of this paper. Energy use statistics in Africa reveal a worrying scenario, with 13% of the global population, consuming only a 3% share of global electricity Furthermore, just 25% of Africans have access to electricity, with more than 70% of Africa is dependent on traditional biomass fuels (African Rift Geothermal, 2018) The Democratic Republic of Congo is located in the western branch of the East African, Rift System (EARS); its entire eastern border runs North to South Kivu beside Uganda, Rwanda, Burundi, and a part of Tanzania, For all Africa, eastern branches of EARS has geothermal energy but has yet to harvest and conduct research in the area within the land occupied by Kenya and Ethiopia, geothermal power has already been developed. Rwanda and Uganda have a certain expertise in geothermal located in Africa. From reports over the last two years. The DRC is still in prospection and identification of springs and many of them are located in areas boarding the rift valley in Maniema-South and North Kivu, however, some springs are identified in the west of the country with origins connected to old volcanoes. In the central Democratic Republic of Congo is blessed with an abundance of hydropower. Although the distribution of populations and cities don’t allow all to use Inga hydroelectricity due to its western location in the nation, So it's necessary to explore alternative energy sources that are geographically proximate such as geothermal sites such located near the spring in Kivu, besides, the environment questions must be taken in the center of all solutions of actual society. The use of geothermal energy in the case of generation involves no combustion on the ground because it uses magma heat energy from the inside the earth. It emits very little carbon dioxide into the atmosphere which is effective against in the context of global warming. Differentiating itself from hydropower, it's not affected by water deficiency; making geothermal generation advantageous (Mitsubishi Hitachi Power Systems, 2018). As geothermal steam contains corrosive gases and impurities such as silica, salt, solid particles, steam turbine design for geothermal plants has to be not only highly efficient but also highly corrosive resistant (Mitsubishi Hitachi Power Systems, 2018). The present paper is dedicating firstly an identification to springs chemical analysis. At the end of the paper, some points of potential views can be taken in the North-Kivu and South Kivu.

2. Location The Albertine graben is a part of the Western branch of the East African Rift System (EARS) commonly known as the Western Rift Valley (Godfrey Bahati, 2006). The D.R.C's geology consists of an exposed pre-Cambrian basement around the central cuvette and the western branch of the East African Rift System in the Eastern part of the country. In the Rift graben, the basement is overlain by intercalating tertiary sediments. The region of the Rift has a markedly higher heat flow than the surrounding Pre-Cambrian terrain. Within the Rift Valley, there are thick layers of late Tertiary and Quaternary sediments; freshwater and saline crater lakes; volcanic; and plutonic bodies have been identified beneath L. Albert and L. Edward (EDICON, 1984)

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The DRC geothermal areas are mostly located in three axes Kahuzi-Biega area, Virunga volcanic field, and Rwenzori area with some small points of lesser value in the country. These areas are given priority because of their volcanic and tectonic features indicated a strong heat source and permeability. The South Kivu geothermal prospect is located in the Kahuzi-Biega Volcanic Field between Lakes Tanganyika and Lake Kivu and around Bukavu town, (Figure 1). The geology is dominated by basaltic flows craters in correlation with granitic and gneissic rock below. The age of the volcanic activity has been estimated at Pleistocene to Holocene (Musisi, 1991). Geothermal surface manifestations are typically hot springs. The volcanism is essential of alkalic type and comprises all classic terms such as ankaratrites, basanites, hawaiites, mugearites, benmoreites, trachytes, and phonolites. Tholeiitic have been mentioned as well. More than 500 and 3,000 m of sediments are known located in the northern deep part of Lake Kivu and Lake Tanganyika, suggesting respective Pliocene and lower Miocene (20 M.A.) ages. Both lakes were probably closed till recently Eocene. The first important outflow of Lake Kivu is dated 9,500 BP and the Tanganyika more recent one would be of historical age and probably from 1878 till recent time. More than 1,500 m of sediments are known in the Ruzizi plain (ILUNGA Lutumba, 1991). D.R.Congo is one of the central and great African countries, it contains part of the African Rift in its West branch, the geothermal area is a father distance from the Northern area part around Albert Lake from Rwenzori Mountain in North Kivu to the South around Tanganyika Lake over 1500Km longer. The center of this zone is a location of volcanic fields with two active, Nyirangongo and Nyamulagira both in DRC. This area is boarded by Rwanda- Burundi-Uganda in East and DRC in West Fig1. The center of the Congo Geothermal field is exposed to Seismic activity with the epicenter located in Kivu Lake, while in the North of Kivu lake basin to volcanic activity last occurred in 2002. All of the geologic terrains described above exhibit hydrothermal activity, except for the fumaroles of Nyiragongo and Nyamulagira volcanoes, all other known hydrothermal features in D.R.C, are thermal springs. All of the features are found in the Eastern part of the country. None are reported to occur to the West of 24OE longitude. A part volcanic origin, the distribution of most of the thermal springs large-scale tectonic affiliation to the highlands of Eastern DRC.

3. Samples and sampling Referring to table N°1, the highest percentage of known springs in the Democratic Republic of the Congo are located in North Kivu. The geothermal of the country is deduce from the hot water because fumaroles were rare. Some of them are located not far from the Kivu Lake, in Masisi and Kabare,, and long the fault as seen in the geological field. The heatThe heat from the ground can be used as an energy source and is found in many regions of the world, especially along tectonic plate boundaries or at places where the crust is thin enough to let heat through. The most common way of capturing energy from geothermal resources is to tap into naturally occurring hydrothermal convection systems, where cooler water seeps into the earth's crust heated up within a reservoir (TURBODEN S.P.A).

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4. Analysis For all data in this paper, some parameters were studied in situ, the pH and color of samples, while others are deduced from laboratory studies. The absence of facilities analyzes kind data in the country lead us to refer to outside universities for more conclusive analysis, unfortunately, none could participate in measurements and analyzes samples. In this paper, we used also sued historical data in the study.

5. Results and Discussion Each geothermal power plant is unique and its design has to be adapted to geothermal resource characteristics with local conditions, geothermal power plants are very complex projects, and integrating design is therefore the key to success. Direct hearting is actually one the oldest and most common forms of geothermal utilization, with applications of use in space heating, balneology, horticulture, and various industrial uses (VERKÍS Energy,2018).

African demand for energy is increasing, yet its ability to generate adequate energy to serve the needs of its growing population, as well as to meet the demands of globalization and industrialization, is still relatively poor. On the other hand, the region has an abundance of alternative sources of renewable, energy resources including hydropower, wind, geothermal, solar, and biomass, whitch, if tapped into, can catalyze the country's economy, social, and environmental development. All Africa is endowed with more than 20GW of geothermal power in the East African rift valley (African Geothermal Centre for Excellence, 2018).

A study of ODHIPIO; MUNGUYOLEYI, , (2017-2018) in the analyzed sites in Rwénzori and found that the thermal waters emerge with temperatures that vary between 37 ° C to the southeast in Kambo and 54°C in the center to Masambo; they are considered mesothermal. With waters, at near-neutral pH (7˂pH˂7,2).

VIKANDY et al, 2006, found that the Na-K geothermometers suggest underground temperatures range of 150 to 270ºC in North Kivu geothermal areas and 275 to 369ºC in South Kivu.

Figure 1 Location of Springs around Lake Kivu, analyzed google view 5.1 Geological data

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The Western rift is a region occupied by diverse tectonic regimes, the northern areas lie in the Archean terrain belonging to the Congo craton, and lithologies within of age about Paleo- to Meso-Proterozoic orogenic belts make up its middle and Southern parts while in Southwestern branches developed Neoproterozoic lithologies. In addition to its main conspicuous physiographic expression lying between D.R.C and its Eastern neighbors, the greater Western rift system also has several secondary rifted and faulted zones on its Western side extending up to the eastern margin of Congo craton, this tectonic regime accounts for a great majority of the hydrothermal features of the country (Getahun Demissie, 2001). A distinctive feature of the Western Rift is that it’s segmented, and is comprised Rift zones, mostly half grabens which are separated from each other by Rift-transverse faults, Quaternary volcanism took place solely along these faults while the interior parts of the Rift segments remain a magmatic, In D.R.C,, the Virunga and Kahuzi-Biega volcanic provinces are, from North to South, found between Lakes Eduard, Kivu and Tanganyika Rift zones, To the North, the Toro-Ankole volcanic province in Uganda separates the Rutangeri and Albert rift zones, The high Mitumba Mountains region of Eastern D.R.C is part of the "African Superswell" which has undergone the most thermal uplift. The Ubendian basement terrain reaches 3,200m elevation along the Western Rift margin on the Western side of Northern of Tanganyika Lake, This is the highest standing basement terrain of Africa attributed to thermal uplift, Between Bukavu city and Kalemie area about 400km, the Western Rift exhibits a complex structural pattern where faults of its three arms interact: the Lake Kivu rift zone as Northeastern termination of the rift branch at the Aswa shear zone in Uganda; the Tanganyika-Rukwa- Malawi (TRM) Rift zone which trends NW-SE to NNW-SSE as Southeastern arm, the northern L, Tanganyika basins and links the above two rift arms and the Ruzizi rift zone: N-S oriented structure which host the Ruzizi River and serves as linking of the two rifts. While the preceding accounts for the tectonic control on individual thermal spring occurrences, their general distribution in the key region affected by the above fault systems may be viewed in terms of the larger scale of crustal structural control, The Eastern D.R.C, is structural old and might generally dating from Gondwana supercontinent rifting, It's the last shearing can be due to the late Carboniferous to Cretaceous, The dominant structural trends are parallel to its lithology stratification in the same places- oriented NW-SE and vary around NE-SW. In some cases, the locations of thermal spring activity along fault zones and in the graben structures which house river basins, it is evident that faults serve as the preferred paths for thermal fluid flow from depth. 5.2 Results

Table 1: chemical composition N° Samples pH SO4 Na K Ca Mg T°c F Br NO3 NH4 Li HCO3 Cl 1 Mayi ya Moto 1 8,94 94,7 - - - - - 4540 1120 478 2730 127 1 0,9

2 Mayi ya Moto 2 8,1 100 21 2,1 5,9 2,6 3400 1035 400 2170 117 9,6 1,2

3 Mayi ya Moto 3 8,2 96,4 25,5 2,5 0,08 4,5 3 5069 1140 480 2745 100 1,1 2

4 Mayi ya Moto 4 7,99 94,5 25 2,4 - 6,2 2,6 4927 1070 590 2660 97 2,4 1,2

5 Tingi 1 8,42 20 2 0,75 4,5 0,77 2,8 2990 275 80 830 165 70 120

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6 Tingi 2 6,9 30 1,7 10 3,5 5,96 3,1 2800 276 78 785 149 37 134

7 Tingi 3 6,68 29,2 1,9 0,63 - 2,1 3,3 2795 284 90 787 141 48 137

8 Tingi 4 6,97 30 1,65 0,85 0,35 1,33 3,1 3080 305 90 770 142 170 124

9 Tingi 5 6,68 30 1,25 0,87 0,5 1 3 2654 311 95 812 142 157 126

10 Kisuma1 6,2 38,5 1,1 0,02 0,35 0,19 0,1 423 9 24 33 29 57 32

11 Kisuma 2 6,5 39 0,5 - 0,05 0,06 0,7 454 11 29 34 26 59 37

12 Kisuma spring 6,8 19,5 15 - 0,25 0,22 0,02 4259 6 12 18 23 48 15

13 Katale 7,63 1,5 0,05 0,65 0,04 0,01 401 35 4 52 61 45 17

14 Bukomo 6,85 18 2 0,01 8,5 0,04 0,01 203 4 10 14,75 19 35 14

15 Nyabugezii 6,95 1,2 0,05 0,09 0,77 0,11 431 3 5 52 72 50 15

16 Kambo 6,97 40 3,5 3,1 1,63 - - 118 700 1104 243 360 380

17 Masambo 7,63 54 6,65 0,44 O,64 - - 100 615 750 113 558 726

18 Mutsora 7,8 57 6,65 0,44 0,64 - - 132 655 1028 123 520 380

19 Kankule 3 7,33 70 1,88 O,12 0,65 nd 0,32 976 60 23 222 65 40 60

20 Kankule 4 6,77 67 1,82 0,1 0,15 nd 0,35 1098 53 23 231 71 46 62

21 Mahvunza 1 7,24 47 1,55 0,05 0,05 nd 0,27 880 46 16 172 55 86 49

22 Maziba 1 6,47 40 0,33 0,05 0,05 nd 0,24 1010 40 17 120 24 117 65

Ions analysis results are carried in Table 1. Interpretation is in a number of different ways, the ternary diagrams are used to classify samples and name them, histograms are used to illustrate the ions evolutions by comparing two or more simultaneously. Sulfate concentration correlated with chloride shows a good relation in the waters sampled from the Paka geothermal prospect. It might be expected that the hot waters might have relatively high Sulphate content in a number of springs and can result from sulfide oxidation by atmospheric oxygen infiltrated in faults or other holes. In the same case, sulfide oxidation occurs in the shallower depths as the deeper hotter fluids ascend to the surface and mix with shallower groundwaters to give much-modified water composition. It is conceivable that the waters that emerge in the boreholes are mixed waters in which case atmospheric oxygen in the cold- water component was involved in converting the sulfide to Sulphate . Figure 2a shows the mixing plot of Magnesium Vs Sulphate . High concentrations of Magnesium in HOT and COOL springs are a good indicator of ground water or surface water. The Rwenzori area is a good indicator of ground or surface waters which could be diluting waters with higher temperatures. The waters with higher temperatures are waters towards the Kambo and or Mutsora area which could have a higher concentration of Sulphate as a result of oxidation of sulphide. Figure 2 b shows the Mangesium Vs Sulphate correlations. The highest concentration of chloride and Sulphate at Mayi ya Moto and Rwenzori springs are possibly influenced by magmatic HCl and SO2 input. The lowest values at others are

Kambale & Makabu reflecting little input from lithological sources (evaporates, Sulphate -enriched) for these parameters.

800 800 Rwenzori Rwindi Rwenzori 600 springs springs 600 Rwindi 400 400

200 200 Tingi others others Tingi 0 0 0 500 1000 1500 0 200 400 600 800

Figure 2: Chloride; Mangesium Vs Sulphate in springs of DRC

It is interesting to observe that the boreholes with higher temperatures also happen to have higher chloride and Sulphate concentrations except for some springs in DRC, the case of Tingi, and some Kisuma's. A High t°C-Sulpate- chloride correlation is shown in Figure 3.

Figure 3: Evaluation of Na-K-Mg content of DRC geothermal springs

5.2.1 Classification of samples For the thermal classification, ternary diagrams are used to classify geothermal water based on major anion concentrations. figure 4 indicates the analysis result.

Figure 4: Evaluation of Na-K-Mg content of DRC geothermal springs

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According to the figure above, most of DRC geothermal districts are high Magnesian and are immature waters. According to Taramaeli T. Mnjokava (2007) this could mean they have a high proportion of cold groundwater and have not attained equilibrium, for such waters, the application of solute geothermometers to estimate temperature is not suitable. The only exception is Mayi ya Moto springs whose Sodium concentration is dedicated to the volcanic rocks wash during the ascendance event. The rich syenitic formations in the belt is unfortunately put in doubt to finance thee concentration. At another side, the use of Chloride-Ssulphide-Carbonous ternary diagram has been used to have a great idea about the concentration of each one, off course, this diagram showed that all waters from springs are rich in HCO3 around 70 to 98,5% and can be classified as peripheral waters that may have mixed with cold groundwater or CO2 from a magmatic source. Referred to in figure 5.

Figure 5: Cl-SO4-HCO3 ternary diagram of DRC geothermal springs

5.2.2 Geothermometry The importance of fluid geothermometry is a key indicator of the geochemistry of thermal areas and relies on the fact that the temperature on which reactions depend of certain mineral phases concentration in particular certain elements. The use of cation and silica-based geothermometry is based on the assumption that chemical equilibrium is obtained between water and rock at elevated temperatures (Opondo K. M, 2004). We tried to apply some geothermometers to thermal waters in the DRC geothermal areas and they are constrained by the fact that most of the dissolved solids load in these waters appears to have been acquired by travertine dissolution rather than by the interaction between water and rock, the case of Rwenzori and Kisuma. On another hand, part travertine, the volcanic evaporitic, and pyroclastic (cendre-scories) have been altered by Atmospheric oxygen, the case of Tingi is a case. Reducing the error, we referred to apply various geothermometry functions to the thermal waters sampled in the prospect area, formula (1), (2), (2). In this paper, the used ternary diagram to evaluate thermal waters is the Sodium-Potassium- Magnesium for suitability of solute geothermometry application. This is shown in Figure 4. The Na-K geothermometers are best applied to thermal waters that are chloride rich. For lower temperature waters that have had long residence times, the Na-K function may be applicable. It can give indications regarding the deeper parts of the system in comparison to

Kambale & Makabu the silica-quartz geothermometer. The Na-K-Ca geothermometer works under the same conditions as the Na-K but extends the temperature range down to between 120 ˚ and 200˚C (Opondo K. M, 2006). Only Na-K is applicable because Na-ca-Mg is not applicable due to its calculation results very low.

1647 4 T°C= 푁푎 푙표푔 퐶푎 -273, avec β= , Na-K-Ca (1) log( )+훽[ √ +2,06]+2,47 3 퐾 푁푎

1217 T°C = 푁푎 − 273. Na-K (Fournier, 1979) (2) 1.483+log( ) 퐾

855,6 T°C = 푁푎 − 273,15. Na-K (Truedell, 1973) (3) 0,857+log( ) 퐾

1390 T°C = 푁푎 − 273 Na-K Giggenbach, 1988) (4) log( )+1,75 퐾 where Na, K, Ca are Sodium, Potassium, Calcium The (1) is in the application of this geothermometer: i) Calculate log (√퐶푎) +2.06 ; if its value is positive, then use β=4/3in the formula in 푁푎 determining the temperature. If that calculated temperature is < 100˚ C, then this temperature is appropriate. ii) If the β=4/3 calculated temperature is > 100˚C or log (√퐶푎) +2.06 is negative, then use β = 푁푎 1/3 to calculate the temperature.

Table 2. The calculated temperatures by some formula in the geothermal area. Site T (1973) F (1976) G Site T (1973) F (1976) G (1988) (1988) Mayi ya Moto 1 117,6 159,2 177,9 Kisuma spring 866,8 611,0 572,7 Mayi ya Moto 2 129,4 169,3 187,5 Katale 813,0 587,8 554,0 Mayi ya Moto 3 99,4 143,5 162,9 Bukomo 872,1 613,3 574,5 Mayi ya Moto 4 99,6 143,6 162,9 Nyabugezii 922,3 634,0 591,0 Tingi 1 275,8 284,0 293,9 Kambo 291,8 295,5 304,3 Tingi 2 268,8 279,0 289,3 Masambo 236,4 254,9 267,4 Tingi 3 260,3 272,7 283,7 Mutsora 207,7 233 247,2 Tingi 4 264,5 275,8 286,5 Kankule 3 342,3 331,7 336,7 Tingi 5 256,8 270,2 281,3 Kankule 4 351,8 336,9 341,4 Kisuma1 663,8 517,7 496,6 Mavinza 1 358,6 342,2 346,1 Kisuma 2 605,7 487,8 471,7 Maziba 1 277,0 284,7 294,5 These geothermometry temperatures compare quite well with those of the Na-K function (Giggenbach, 1988). The Na-K-Ca geothermometer often provides temperatures that are lower than the Na-K function. Under normal conditions, the Na-K-Ca geothermometer

Kambale & Makabu usually gives slightly higher temperatures than the Na-K geothermometer for boiling hot spring waters. The loss of potassium from the solution will lower the Na-K-Ca temperatures. Loss of calcium will counter potassium loss through precipitation. Some loss of potassium through feldspar precipitation could cause potassium to decline in concentrations. Na-K-Ca geothermometer gives a lower temperature than those of Na-K.

1000 900 800 700 600 500 400 Truesdell (1973) 300 200 Fournier (1976) 100

0 Giggenbach(1988)

Katale

Tingi 1 Tingi 4 Tingi Tingi 2 Tingi 3 Tingi 5 Tingi

Kambo

Bukomo

Kisuma1

Mutsora

Kisuma 2 Kisuma

Maziba 1 Maziba

Kankule 3 Kankule 4 Kankule

Masambo

Mavinza 1 Mavinza

Nyabugezii

Kisuma spring Kisuma

Mayi ya Moto 2 ya Moto Mayi 3 ya Moto Mayi 4 ya Moto Mayi Mayi ya Moto 1 ya Moto Mayi 9000 8000 7000 6000 5000 4000 3000 2000 Giggenbach, 1988(°C) 1000 Deep (m)

Katale

Tingi 1 Tingi 2 Tingi 3 Tingi 4 Tingi 5 Tingi

Kambo

Kankule

Bukomo

Kisuma1

Kankule

Mutsora

Kisuma 2 Kisuma

Maziba 2 Maziba

Mahyuza

Nyabugez

Masambo

Kisuma spring Kisuma

Mayi ya Moto 3 ya Moto Mayi 4 ya Moto Mayi Mayi ya Moto ya 2 Moto Mayi Mayi ya Moto ya 1 Moto Mayi Figure 6: Comparison of two equations evolution results

5.2.3 Tank Depth Estimate Geothermometry is a tool for estimating the depth of geothermal reservoirs and the temperature of the last chemical or isotopic equilibrium before emergence (Boudoukha, A. et al, 2012). According to this geological, the information of the reservoir is collected by interpretation of the geothermal emanations chemistry, one sees their deep waters and gases. To all this, these agents carrying the history and composition of the tank are contaminated. With this combination with meteoric waters and exogenous rocks, the temperature is diluted with the source it is less strong than that of the reservoir. The increase of the temperature according to the depth is called geothermal gradient or temperature gradient, on average it is 10 ° C for 100m (Meyer, M., 2009).

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Figure 7: Temperature Change with Depth in Various Regions (Meyer, M. 2009)

Considering the temperature gradient of the rift found on this graph proposed by Meyer, M., in 2009, that is to say, an increase of 10 ° C after 100m. The temperature of the reservoir is however known starting from the notion of the geothermal gradient; varying on the globe. The Kivu, volcanic being of 10C / 33m is 100C / 100m.

Table 3. Estimate of reservoir temperature and deep North Kivu Site T°C Deep Site T°C Deep Site T°C Deep (m) (m) (m) Mayi ya Moto 117,6 229 Tingi 3 260,3 2308 Katale 813, 7680 1 0 Mayi ya Moto 129,4 294 Tingi 4 264,5 2345 Bukomo 872, 8541 2 1 Mayi ya Moto 99,4 31 Tingi 5 256,8 2268 Nyabugez 922, 8823 3 3 Mayi ya Moto 99,6 51 Kisuma1 663,8 6253 Kambo 291, 2511 4 8 Tingi 1 275,8 2558 Kisuma 2 605,7 5667 Masambo 236, 1824 4 Tingi 2 268,8 2389 Kisuma 866,8 8473 Mutsora 207, 1507 spring 7 South Kivu Kankule 342,3 2723 Kankule 351,8 2817 Mahyuza 358, 3116 6 Maziba 2 277,0 2370

The Rwenzori sites show a depth of around 1507 m for the Mutsora site, 1824 m for the Masambo site and 2511 m for the Kambo site whereas in the Goma region around

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Nyiragongo and Nyamulagira volcanoes are between 230 to 295 m for the site. The site of Rwuindi (Mayi ya Moto) is seen as an anomaly that is not worth the trouble but whose assertion of a flaw is probably or a hypothesis. The Sake region has a reservoir whose depth is between 2268 and 2558m deep. The thermal sites of Kisuma in Masisi come from the reservoir whose depth varies from 5667 to 8473 m. Katale and Ruthsusru is reservoirs with a geothermal roof depth of 7680m. The thermal spring of Nyabugezi in the same territory has a reservoir depth estimated at 8823m.

From these estimates, conclude the temperature of the hydrothermal emanations on the surface does not correlate directly with that of the reservoir, the sites of Mayi ya Moto in the metamorphic outcrops is 94.5 at 100 ° C that high temperature In the region shows a Na-K geothermometry a superficial and warm reservoir. Whereas Nyangezi, with 40 ° C of outcropping is hot and, deep. We confirm that the least temperature is not only at this depth but also at the lithology. The sites of the sedimentary basins are doped on the surface.

6. Conclusion This paper presents a preliminary chemical analysis and its results witness a geothermal potential that exists in the Eastern Democratic Republic of the Congo as predict in past studies. Using ions geothermometry in the different equations, hottest springs Mayi-yamoto is a site referring to his surficial data in North Kivu. Besides, this site is the only springs sampled which has an equilibrium temperature and a minimum of carbonadoes-Sulphide- chloride. The analysis estimates these reservoirs at 162,9ºC to 177,9ºC from Giggenbach (1988) while Fournier (1976) 143,6 ºC to 169,3 ºC and Truesdell (1973) 99,6 ºC to 129,4 ºC. Referring to the Truesdell Na-K equation results, minding the permeability of volcanic rocks and structural analysis, the thermic gradient, the reservoirs is estimated to be about 30 to 295 meters. This is due to chemical analysis to the highly deep investigation, on the potential springs, SO2 geothermometers except for K-Na-Ca, another diagram such as Ca-B-Li are best to be used. In-situ CO2 and H2S gas survey is a key of evolution. This led us to think about geophysical surveys missed isotoping quantifying.

ACKNOWLEDGEMENT The authors want to present special thanks to Professor MAMBO VIKANDY Hilaire from Dean of Rwenzori State University science faculty who’s the pioneer and link of DRC to whole geothermal in the world. Our thanks go directly to the Steering committee for the Development of Geothermal Resources in North Kivu (CPDRG) for integrating us among the researcher team.

REFERENCES African Geothermal Centre for Excellence, Excellence is an art won by training and orientation, unedited African Rift Geothermal, African Rift Geothermal Development CONCEPT to ACTION seizing the moment: Investing in geothermal energy for sustainable development, 7th conference, P2

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Getahun Demissie, geothermal resource indications of the geologic Development and hydrothermal activities of d.r.c, ARGEOC3 Djibouti, 22 – 25 November 2010 Godfrey Bahati, Isotope hydrology studies of Katwe, Buranga and kibiro geothermal systems, Uganda Godfrey Bahati, 2006, Geothermal Energy Exploration in Uganda, Country Update, ARGeo ILUNGA Lutumba, 1991, Morphologie, volcanisme et sédimentation dans le rift du Sud-Kivu in Bulletin de la Société géographique de Liège, 27, Pg 209-228 Mambo V. S and all, 2012, Geochemical study of thermal springs in Eastern D.R. Congo, ARGeo-C2 Mitsubishi Hitachi Power Systems. Geothermal Power Plants PSBO-01GP09 E1-A-O, (1.5) 18-6, ZEG,P2, unedited Mitsubishi Hitachi Power Systems. Geothermal Power Plants PSBO-01GP09 E1-A-O, (1.5) 18-6, ZEG,P9 , unedited ODHIPIO A. D, MUNGUYOLEYI YOSSA. H, 2017-2018 Etude Géologique Des Sources Thermales Du Secteur De Ruwenzori ; Bachelor Thesis, Rwenzori State University, DRC Opondo Kizito Maloba, Mixing trends and solute geothermometry of borehole Waters from the paka geothermal prospect. Kenya Electricity Generating Company. Pre-ARGeo C7, Conference shorts courses, Kigali / Rwanda 29-30 October 2018 Taramaeli T. Mnjokava, 2007, Interpretation of exploration geochemical data for geothermal fluids from the geothermal field of the rungwe volcanic area, sw-tanzania, Geothermal Training Programme orkustofnun, grensásvegur 9, number 14 is-108 reykjavík, Iceland, UNITED NATIONS UNIVERSITY TURBODEN S.P.A, Clean Energy ahead, 16-COM.B-2-rev.3 VERKÍS Energy, Icelandic consultancy for renewable energy, P2, unedited