Geological characteristics of Kibiro, Uganda & Ngozi- Songwe, - - PowerPoint PPT Presentation

geological characteristics of
SMART_READER_LITE
LIVE PREVIEW

Geological characteristics of Kibiro, Uganda & Ngozi- Songwe, - - PowerPoint PPT Presentation

Geological characteristics of Kibiro, Uganda & Ngozi- Songwe, Tanzania geothermal prospects Western Branch of EARS Workshop, Kigali, Rwanda March 9-11, 2016 Kenneth B. (Keg) Alexander, Geologist Middle Earth Geoscience, Auckland, New


slide-1
SLIDE 1

Geological characteristics of Kibiro, Uganda & Ngozi- Songwe, Tanzania geothermal prospects

Western Branch of EARS Workshop, Kigali, Rwanda March 9-11, 2016

Kenneth B. (Keg) Alexander, Geologist Middle Earth Geoscience, Auckland, New Zealand keg@middleearthgeo.co.nz

slide-2
SLIDE 2

Presentation agenda

  • Project background and organization
  • Objectives
  • Areas of interest and regional setting (Kibiro and Ngozi)
  • For each project:
  • Summary of previous geological surveys
  • Current approach and focus
  • Preliminary understanding of geological conceptual model

2

slide-3
SLIDE 3

Project background and

  • rganization
  • In 2015, requests for technical assistance submitted by:
  • Uganda Directorate of Geological Survey and Mines (DGSM)
  • Tanzania Geothermal Development Company (TGDC)
  • Funding by African Rift Geothermal Development (ARGeo)
  • Implementation by UN Environment Programme (UNEP)
  • Technical advice and equipment provided by Geothermal

Development Company of Kenya (GDC)

  • 3 advisors: Bill Cumming, Luigi Marini, Keg Alexander

3

slide-4
SLIDE 4

Project objectives

  • Develop an integrated conceptual model for each site

using geology, geochemistry, and geophysics

  • Review of existing surveys
  • Collection of new data
  • What are the potential heat sources and fluid pathways?
  • Recommend locations and targets for exploration wells
  • Tentative project completion date: May 2016

4

slide-5
SLIDE 5

Areas of interest

  • Kibiro
  • SE shore of Lake

Albert

  • Ngozi
  • Part of the

Rungwe Volcanic Province at intersection of 3 rifts

5

Kibiro Ngozi

Source: Chorowisz, 2005

slide-6
SLIDE 6

Geological survey focus areas

  • Thermal manifestations
  • Evidence of a geothermal system
  • Structural geologic setting
  • Evidence of potential fluid pathways
  • Evaluation of current stress regime
  • Petrography and XRD
  • Evidence of hydrothermal alteration
  • Recent or relict?
  • Hydrogeology
  • Understanding groundwater flow, and recharge and discharge areas

6

slide-7
SLIDE 7

Kibiro – overview

  • Kibiro hot springs located in sediments at foot of eastern

escarpment of Lake Albert graben (northernmost rift basin)

  • Extension related normal faulting has resulted in

significant topographic features – footwall rises more than 350 m above rift basin

  • NE-SW escarpment divides the

study area into two entirely different geological environments

7

slide-8
SLIDE 8

Kibiro –

  • verview

8

Source: Ring, 2008

Kibiro

  • To the SE, the geology is

dominated by Pre-Cambrian crystalline basement: granitic gneisses, schists, quartzites

  • To the NW, the rift valley consists
  • f sequences of sediments, up to

5.5 km thick

  • No volcanic rocks near Kibiro;

closest location are Rwenzori Mts

slide-9
SLIDE 9

Kibiro –

  • 9
slide-10
SLIDE 10

Kibiro – previous geological studies

  • 1993: DGSM and UNDP. Focus on geology and
  • geochemistry. Heat source from rift basin sediments?
  • 1999-2002: DGSM and IAEA. Focus on isotope hydrology.

Recharge from higher ground. Heat source from basement?

  • 2004-2005: ICEIDA. Focus on geology, TEM, gravity and
  • magnetics. Low resistivity and gravity anomalies point to

possible heat source in basement to SE?

  • 2012-2013: DGSM. Focus on Toro-Bunyoro Fault, thermal

manifestations, and mafic dykes. Upflow through main fault scarp?

10

slide-11
SLIDE 11

Kibiro – heat source

  • ptions

11

NW SE DRC Uganda

5 km 1500 m Base Kisegi Base Kaiso Pre-Rift Basement Based on Karp et al (2012)

Kibiro hot springs

Rift basin sediments Pre-Cambrian Basement Pre-Cambrian Basement Pre-Cambrian Basement

? ? ?

slide-12
SLIDE 12

Kibiro – TG wells

12

2006: DGSM and ISOR drilled 6 TG wells

slide-13
SLIDE 13

Kibiro – results of TG wells

  • Max T = 35.1 °C
  • Thermal gradients low; continental average: 25 – 30 °C/km
  • No hydrothermal alteration observed in any cuttings
  • Low resistivity anomalies not caused by heat anomaly

13

Well No. Location (WGS84 Zone 36 N) Elevation (masl) Depth (m) Maximum temperature (C) Thermal gradient (C/km) Easting Northing KIBH-1 305960 179150 1039 300 29.4 16.0 KIBH-2 306620 180140 1023 300 29.2 16.0 KIBH-3 303820 179200 959 300 29.7 16.0 KIBH-4 306335 184074 914 262 35.0 27.3 to 31.3 KIBH-5 305420 183420 931 300 35.1 22.0 KIBH-6 304800 179110 1000 290 29.4 16.0

slide-14
SLIDE 14

Kibiro – thermal manifestations

  • Kibiro hot springs
  • Main area is Mukabiga located near intersecting faults at base of

escarpment

  • Max T = 86.5 °C, total flow = 4 L/s, gas bubbling and strong H2S smell, oily odor
  • Second group of springs downstream (Mwibanda)
  • Range of T’s: 33 to 72 °C, total flow = 2.5 L/s
  • Muntere springs occur in pits excavated for salt production
  • Max T = 39.5 °C
  • No other active hot springs known to exist in Kibiro study

area nor along southeastern margin of Lake Albert graben

14

slide-15
SLIDE 15

Kibiro – other manifestations

  • Sulphur deposits indicate that some H2S is being released
  • No active fumaroles
  • Deposition of secondary minerals of uncertain origin in Kachuru and Butiaba
  • Surface alteration
  • Limited areas of argillic alteration (major clay type is smectite)
  • Smectite can form due to weathering or low T hydrothermal alteration
  • New samples currently being analyzed
  • Oil seeps
  • Petroleum-bearing source rocks present
  • Migration pathways to surface

15

slide-16
SLIDE 16

Kibiro – petroleum in Lake Albert basin

  • Potential source rock kitchen (area of petroleum

generation) on DRC side of Lake Albert

  • Nearest oil well is 15 km to NE (Taitai-1)
  • - Max T of 61 °C at depth of 971 m

16

Source: Tullow, 2007

Kibiro

slide-17
SLIDE 17

Kibiro – structural geologic setting

  • Lake Albert has undergone substantial tectonic

movements and thick sediments have been deposited

  • Full, asymmetrical graben; shallow lake, max depth = 58 m

17

Source: Karp et al, 2012 Note: Seismic Line 57 tied to Well Waki-B1 in footwall of Butiaba Fault for stratigraphy

slide-18
SLIDE 18

Kibiro – structural geologic setting (cont.)

  • Recent tectonic history
  • Rifting originated in late Oligocene or Early Miocene (~23 Ma)
  • Compression during mid-Miocene (~15 Ma)
  • Second phase of rifting during Pliocene (~2.6 to 5.3 Ma)
  • Compression during the Pleistocene (~0.01 to 2.6 Ma)
  • Present day: normal faulting regime (extensional)
  • Lake Albert rift developed as a pull-apart in a sinistral-

transtensional environment

  • Complicates interpretation due to different stress regimes

18

Tectonic history source: Delvaux & Barth, 2010

slide-19
SLIDE 19

Kibiro – current stress regime

  • Normal faulting with WNW–ESE extension (based on focal

mechanisms)

  • SHmax direction is NNE-SSW

19

Kibiro

slide-20
SLIDE 20

Kibiro – influence of faults

  • N. Toro Bunyoro Fault
  • Butiaba Fault
  • Accommodation and

transfer zones = increased fracture density

  • Deformation of upper

crust between faults influenced drainage and sedimentation

  • Minor faults intersect

Toro Bunyoro Fault at Kibiro

20

Source: Karp et al, 2012

Kibiro

slide-21
SLIDE 21

21

Kibiro – minor fault intersections Kachuru fault – NNE-SSW Kitawe fault – WNW-ESE

slide-22
SLIDE 22

Kibiro – hydrogeology

  • Regional uplift of escarpment has reversed drainage

systems and helped form Lakes Victoria and Kyoga

  • Lake elevation has decreased ~100 m over past 2,000 yrs
  • Recharge from area above Rift escarpment, through

fractured metamorphics with discharge into lake

  • Well KIBH-4 (~1.1 km SSE of hot springs) encountered high

permeability in fractured rock at depth of 114 m (800 masl)

  • Kibiro springs (639 masl) mix of geothermal water and

shallow brackish water. Likely separate hydraulic connection from groundwater in metamorphics.

22

slide-23
SLIDE 23

Kibiro – status of current geological survey

  • DGSM conducting field surveys with focus on Kachuru and

Kitawe faults and surface alteration – results pending

  • GDC of Kenya analyzing 11 rock samples for thin section

petrography and XRD - results pending

  • Compilation and interpretation of groundwater data -

results pending

  • Meeting with DGSM and GDC in Entebbe to evaluate

recent field results (14-18 March 2016)

  • Integration of data to prepare geologic conceptual model

23

slide-24
SLIDE 24

Kibiro – preliminary geological conceptual model

  • Lake Albert rift basin
  • Rifting led to normal graben faulting and thinner crust
  • Similar to Basin & Range setting
  • Active and deep (>30 km) seismicity beneath Lake Albert
  • Earthquakes >M4.5

since 1900:

24

slide-25
SLIDE 25

Kibiro – preliminary geological conceptual model (cont.)

  • Changes in regional stress regime over past 20 Ma
  • Episodes of rifting and compression
  • Development of pull apart basin with deep-seated, parallel boundary faults
  • Kibiro hot springs
  • Located at intersection of faults
  • Only springs along SE margin Lake Albert rift basin
  • Hydrologic system separate from groundwater flow in metamorphics
  • Oil seeps show fluid migration through nearby sediments

and up N. Toro Bunyoro Fault

25

slide-26
SLIDE 26

Kibiro – preliminary geological conceptual model (cont.)

  • Fluids gain heat through deep circulation beneath Lake

Albert

  • Heated fluids rise to base of sediments in basin and then

up deep-seated rift border fault (possibly Butiaba Fault)

  • Heated fluids flow updip through sediments towards

Bunyoro Fault

  • Discharge at Kibiro springs at zone of weakness

(intersection of Bunyoro Fault and minor faults)

26

slide-27
SLIDE 27

Ngozi – overview

  • Ngozi volcano is part of the Rungwe Volcanic Province in

southern Tanzania

  • Located at triple rift junction of NW-SE trending Rukwa

and Malawi Rifts and the NE-SW trending Usangu Basin

  • Primary geothermal features in the study area:
  • Ngozi caldera lake – thermal water discharges up to 89 °C on lake bottom
  • Songwe River thermal area – hot springs located >40 km WNW of Ngozi,

numerous small and large springs, max T = 75-80 °C, total flow estimated to be 75 L/s

27

slide-28
SLIDE 28

Ngozi – overview (cont.)

28

Songwe

Source: Fontijn et al, 2012

33.5°E

slide-29
SLIDE 29

Ngozi – lithology

  • Travertine – active deposition over past 360 ka
  • Miocene – Recent (past 10 ± 2 Ma) Rungwe volcanics
  • Miocene – Recent lacustrine and fluvial sediments
  • Cretaceous (~66-145 Ma) Red Sandstone Group formed in

rift valleys

  • Permian – Triassic (~200-300 Ma) Karoo conglomerates in

rift valleys

  • Pre-Cambrian (>600 Ma) metamorphic basement (exposed

to NW and SE of RVP)

29

slide-30
SLIDE 30

Ngozi – previous geological studies

  • Tanzanian government (MEM, GST, and TANESCO) in

cooperation with the German Institute for Geosciences and Natural Resources (BGR) completed:

  • 2006-09: GEOTHERM Phase I
  • Comprehensive pre-feasibility study
  • Surveys identified presence of active faults, young volcanic heat source, and a reservoir in basal

volcanics, above the basement metamorphics

  • 2009-13: GEOTHERM Phase II
  • Focus on geophysics (MT and TEM)
  • Bathymetric survey of Lake Ngozi showed high bottom temperatures
  • The conceptual model indicated a >200 °C geothermal

reservoir beneath Ngozi with outflows mainly to Songwe

30

slide-31
SLIDE 31

Ngozi – thermal manifestations

  • Thermal manifestations consist of hot and warm springs, and

cold gas emissions (e.g., intense bubbling at Shiwaga)

  • Can be divided by elevation and locality
  • Warm springs and cold gas (CO2) emissions at higher elevations on flanks of

Ngozi

  • Significant hot spring discharges at lower elevations distal from RVP (Songwe to

NW and Kilambo to SE)

  • No fumaroles are known to occur
  • No thermal manifestations within Ngozi caldera
  • Very little surface alteration
  • Fluid flow controlled by fracture permeability along active faults

31

slide-32
SLIDE 32

Ngozi – thermal manifestations (Songwe)

  • Songwe River thermal area
  • Numerous springs discharge neutral, Na-HCO3 water between 50 and 80 °C
  • Spring locations fault-controlled in general NNW-SSE alignment
  • Spring elevations at Songwe are 30 to 50 m higher than Songwe River
  • Total discharge estimated at 50 to 75 L/s
  • Songwe travertine deposits
  • Springs discharge through extensive travertine deposits, 5 to 70 m thick

covering an area of about 13 km2

  • Travertine overlies Cretaceous Red Sandstone Group
  • Travertine formation possibly due to hot water circulating through 100 Ma,

carbonatite-rich volcanic rocks

32

slide-33
SLIDE 33

Songwe – springs

  • Songwe River

Thermal Area springs

  • Songwe (60 – 75 °C)
  • Madibira (~55 °C)
  • Kaguri (~48 – 67 °C)
  • Ilatile (65 – 80 °C)
  • Over time springs

and travertine deposition moving toward NW

33

Adapted from: Roberts et al, 2004

Songwe Madibira Kaguri Ilatile

slide-34
SLIDE 34

RVP – volcanic activity

  • Late Cretaceous (~70-100 Ma) with Alkali-carbonatitic

magmatism (emplacement of Panda Hill and Songwe scarp)

  • RVP alkaline volcanism began during Miocene (10 ± 2 Ma)
  • RVP volcanoes have been active during Holocene:
  • Rungwe – 1 Plinian eruption ~4 ka and >7 explosive eruptions in last ~4 ka
  • Ngozi – 2 Plinian eruptions in last ~10 ka (Kitulo Pumice and <1 ka Ngozi

Tuff)

  • Kiejo – Effusive eruptions ca. 200 years ago
  • Ngozi lavas are mainly phonolitic-trachytic with some

alkali-basaltic composition at lower elevations

34

Source: Delalande-Le Moullic et al (2015)

slide-35
SLIDE 35

Ngozi – intrusive carbonatite outcrops

  • Panda Hill (113 ± 6 Ma)
  • Songwe scarp (100 ± 10 Ma)
  • Dyke structure 6 – 30 m thick along Mbeya Front fault
  • Outcrops for ~20 km along base of 1000-m high scarp between

metamorphics of Mbeya Range to NE and Songwe river valley to SW

  • Emplaced in a zone of weakness (likely prior rift faulting) during period of

normal faulting regime

  • Implies deep fault connection with near mantle source
  • No thermal features along Songwe scarp (Mahombe springs at N end of

Mbeya Front fault is N of carbonatite outcrop)

35

Source: Brown, 1964

slide-36
SLIDE 36

36

Songwe

slide-37
SLIDE 37

Ngozi – structural geologic setting

  • Development of Western

resulted in major transfer zones between normal rift faults

  • Field investigations show that

faulting in the Rukwa Rift during the Late Cenozoic are normal

  • Regime changes rapidly into

strike-slip faulting in the Rungwe volcanic area at the junction between the Rukwa and Malawi Rifts

37

Source: Corti, 2012

slide-38
SLIDE 38

38

Source: Delvaux et al, 2010

slide-39
SLIDE 39

Ngozi – current stress regime

  • Since the Middle Pleistocene, the stress regime is dextral

strike-slip faulting along (partly pre-existing) NW-SE to N-S faults

  • Compressional stress regime with SHmax in ENE-WSW

direction

  • Focal mechanisms consistent with compressional regime

and associated strike-slip faulting within RVP

39

Source: Fontijn et al, 2012

slide-40
SLIDE 40

Regional stress regime

  • Albertine Rift

(#11)

  • Mbeya

(#16)

40

Source: Delvaux & Barth, 2010

slide-41
SLIDE 41

Ngozi – Mbeya Front- Mbaka Faults

  • Mbeya Front fault to NW of RVP, Mbaka Fault to SE
  • Current tectonic stress regime implies that faults are under

E-W to ENE-WSW horizontal compression

  • Dominant structural features, but are they connected?
  • Near perfect alignment
  • Numerous springs and maars along Mbaka Fault; none along Mbeya Front
  • Carbonatite not found along Mbaka Fault
  • Mbeya Front fault – deep-seated, substantial throw, >1000-m scarp
  • Regardless of connection, Mbeya Front fault is likely a

barrier to horizontal groundwater flow

41

slide-42
SLIDE 42

Ngozi – hydrogeology

  • Ngozi Caldera lake has no surface inlets or outlets
  • Water enters via precipitation or groundwater flow and

discharges by groundwater outflow and evaporation

  • Surface drainage indicative of groundwater flow direction
  • West side of Ngozi Caldera lake drains toward the south
  • Drainage to NW likely captured by Mbaliza River watershed
  • There is a hydrologic divide between Mbaliza and Songwe Rivers
  • Therefore, outflow from Ngozi is unlikely to reach Songwe

42

slide-43
SLIDE 43

43

Source: Kraml et al, 2014

slide-44
SLIDE 44

Ngozi – status of current geological survey

  • TGDC currently evaluating data collected during recent field

surveys – results pending

  • Lithic sample assessment (26 lithic samples)
  • Interpretation of groundwater data
  • Evaluation of depth to basement at Ngozi
  • Updated geological and structural map
  • GDC of Kenya analyzing 50 rock samples for thin section

petrography and XRD – final results pending

  • Meeting with TGDC and GDC in Mbeya to evaluate recent field

results (20-25 March 2016)

  • Integration of data to prepare geologic conceptual model

44

slide-45
SLIDE 45

Ngozi – preliminary geological conceptual model

  • Ngozi
  • Young volcanic heat source; thermal discharge at lake bottom
  • Rungwe volcanics directly overlie metamorphic basement rock
  • Geothermal reservoir likely within Older Volcanics on north flank of Ngozi
  • Outflow likely to NW toward Mbeya
  • Structural and hydrologic barriers to flow from Ngozi to Songwe
  • Songwe
  • Separate, fault-controlled geothermal system
  • Fluids gain heat through deep circulation (likely through SW margin fault of

Rukwa Rift)

  • Recharge likely through fractured metamorphics of Chumwa Range to SW

with possible input from SSE (Panda Hill)

45

slide-46
SLIDE 46

Thanks to Geology Teams at DGSM, TGDC and GDC! Questions?

Keg@middleearthgeo.co.nz

46