Report No. 38 "'."" ." COLONY AND PROTECTORATEPROTECTORATIC 0FOF KENYA GEOLOGICAL SURVEY OF KENYA }-i GEOLOGY OF THE J MWIN‘GIMWINGI AREA, NORTH KITUlKITUI DEGREE SHEET 45, SOUTH-WEST QUARTER (with coloured geological map) byI)y The late A. F. CROWTHER, B.Sc.,B.Sc.. F.G.S. Geologist 1957I957 PRIN'I'EDPRINTED BY THE GOVL-ZRNMFNiGOVERNMENT PRINTER,PRiNI'L-‘R, NAIROBI Prk'c:Price: Sh. If}10 IS! FOREWORDl- { ”Hi“ { )R I) The geological survey of the Mwingi areai] E'L‘ii \'\was\i‘. carried' out by Mr. Crowther as part of the primary mapping of Kenya, with the assistanceL:‘-\|\'l‘ of funds provided under the Colonial ..,‘. I Development and Welfare Act. Before he could\\ LIIL. bring his report to its final stages he was :cmh called up for military training and ...subsequently was retained in the Kenya Regiment. He served with the Regiment in KenyaCilgiz; fromii. :11 the[EN-'- beginning of 1953, but unfortunately lost his life in February, 1954, in ;:a skirmishakii'mixh withuiLEi terrorists.Lei" To prevent undue delay in publication, the first draft of his report hadhmi beenhL‘cu :1completedimr‘icicd and:izui amended on his behalf in 1953, but he had not had the opportunity toin readrun! the- proposed final draft before his death. In preparing the final draft everymu} attemptLlncriip‘a wasuh maden;- where possible to preserve the original outline and the2hr ii'cndtrend ul‘of 1hrthe :iiilhm’sauthor's I.‘Il‘|_!g.i!1\.thoughts. TheEiic aii'cuarea cmleast v!of Muiiigi.Mwingi, :1a \iilugcvillage m‘.on 1!:cthe run-Jroad I'i'nmfrom \iii';Nairobi through Garissa to the \aii’lilui'l‘.Northern Pi'mii‘iccProvince m”of KcnyaKenya ;li‘.'Ciand ItalianHill I‘ Sm‘Somaliland,flziiiiuiui. i‘c-gzimcbecame ki‘H-c.‘known to people in Kenya wi‘non nccuumaccount 01‘of ua prospector'sg‘ui‘mpczloi‘ \ mmrcamp r.and. factory' Jan :1:at \3Nguni:.i Microwhere chalks,kflJi-i‘, . whitening powders and mmcrulmineral pigmentspigmcmx “cu:were prepared.pi'cgmr IUnfortunatelynl'ui‘iiii ': ' littleitlu rim:else (11'of m.-mineral. value' “L- has been foundliquid in 111::the :ii‘cu.area. i\'3..Mr. (Crowther's['U\\ii]L‘!' \ report[1‘ i givesbiwx (Ia i‘i'j-cibrief 'ic-JJIJIEEaccount 01'of the general‘:=Ci’;i] ut‘uiuuxgeology of Elmthe L»district,I. \pi‘gialspecial ampemphasisNix hcii‘wbeing laid|_iiL. mion "asmallfliili: iiILEL'r-ultra-basic" intrusionsii‘;‘.1’ii\iui‘n iiiin |[\its 431151011eastern part.l‘dii. ‘ - \ . L‘.. L' T.The’ intrusions|I13I'Li')iL‘-i1\ are oful‘ 'ia .kind1L! lit-:11that in numerousnumcmm partspuns Hiof the world\xurlii uir'i‘contain valuable‘»'.i|'.:'.mIL‘ metallicmun .i: m.or nun—meldilicnon-metallic minerals,mi Julia. Lindand ilmugiithough lhcii'their prospects11!'(1\]‘¢'J{\ muare not1 'riupcii'ihopeful iin view of the results1x “Iof thethe: T‘['€\C‘H[presentJ HIRE}.survey, 'it ix.is nu:not iinpmsihicimpossible 511:1!that mm:more intensivelunxixu prospectingPac- might revealam cal \I‘Crdiismall dept-Hmdeposits ulof \lici‘.such ulnar-ahminerals Ll\as 11:;magnesitemew-it aandmi .i\i"t‘\1l‘-\.asbestos. Forhii' wmcsome ycmxyears rumoursi'umnui's Innshave persistedpuixislmi ofl‘-i thealt-L- ncwi’rcm‘coccurrence ofu!‘ gnu:coal in thei:. C northerniil‘iiiiC i1 parts|‘-;i!'l~ Miof {hethe kiln]Kitui iiiwz'iui.district. Mr. (.Crowther'm'LhCi' mink"made Ll.a ape-gm!special mam“;investigation[iiit‘l] miof 2.9.:the z'cl‘i“:'{cL‘ireported [iii-JRfinds hall.but, :1\as \‘(3\was Upctlcdexpected J‘I'UIHfrom lhcthe geologyguniog} nl'of Ehuthe LiI‘CLLarea, \\Li\was unableLiiiuhk Into findIii‘iLi Lin}any Era-cctrace v:of gnu!coal uror possiblyi‘iwxibi} coal-bearingg:‘;l|—ht;il'ing beds.iWULiK. ThereiiCl'C canL1H] behe noI‘:I- doubtLinilhi thatIi‘:;':' coalL‘i‘u" foundinul'id in such\UL‘i1 munareas isIx thec relics[-QEiL‘x of war- timeaim-c dumps. WILLIAM\\H Li ‘-.\E PULFREY, Nairobi,\L.i nhi. Chid Geologist. 15th". November,\nxcmhcr 1954.I”. ii‘\i?2\!.‘~CONTENTS PAGE Abstract I-Introduction 1 II-Previous Geological Work 2 III-Physiography 2 IV-Summary of Geology 4 V-Details of Geology.. 5 I. Basement System 5 2. Pleistocene and Recent 10 3. Intrusives 10 VI-Metamorphism 16 VII-Structures 17 VIIT-Economic Geology. 19 1. Basement System. 19 (I) Garnet and sillimanite 19 (2) Limestone and marble 19 (3) Pigments and gypsum 19 2. Ultra-basic intrusions 19 (I) Magnesite. : 20 (2) Anthophyllite asbestos 20 3. Superficial Deposits 20 (I) Sand. 20 (2) Road-metal 20 (3) Building material 20 4. Alleged coal deposits 20 5. Water. 20 (I) Surface water 20 (2) Ground water. 20 IX-References 21 ILLUSTRAH ‘N'! nONS Fig. I.-Physiographic units 3 Fig. 2.-Geological Sketch of Kamuthengi hill I I Fig. "3.-Diagrammatic microscope drawings 12 Fig. 4.-Structures in the Mwingi area. 18 Plate T.-(a) View south from Gai showing peneplains 7 (b) Leucocratic biotite gneiss enclosing melanocratic masses 7 Plate II.-(a) Leucocratic biotite gneiss enclosing folded melanocratic bands 8 (b) Melanocratic biotite-rich band, bent and injected by quartzo-felspathic material 8 MAP Geological map of the Mwingi Area, North Kitui (degree sheet 45, south-west quarter) Scale I :125,000 . .. At end ,... ABSTRACT\BS'I R \( '! TheIM- report'cnn: duxudescribesflwx an.m x-area in the northernAIM-1'»V partmm ofmi the1“; Kamba‘mmflm Native\‘mwc ReserveRcwl'xc 1in central Kenya. It' is‘ approximatelya‘mwn ; 1,200 squareAg ‘7‘mileso in\ extent“1;“! \vandMi is\ l‘wmxigxbounded by latitudes 0° 30' S. and 1° 00' S. and by meridians 38° 00'w E.; and, M 38°w 30' E.} PhysiographicallyI"wj.\1~~ it can be divided into three units:Al m (I)‘111the Mumoni- mountainsT‘IL‘L‘ L1 w“ in‘7 theI'm‘ north-west,14‘72 \“V-(‘L (2) relatively high ground in the west that is‘V\ copsideredLxW"\Lk"k\' toU‘ be\‘L‘ ad remnant[\ZW'K W Nof thesm- sub-Miocenew,.:¥\'mccnc peneplain,:‘cmpkmx which is also represented by the topsmw ofw' \Mmu'cu‘.scattered monadnocksHM :‘mUJ‘wdm ‘Hin the \LMJIILL‘I'lisouthern half :H'iof the area, and (3) a low-lying peneplainLq‘ v.1"! ofM presumed:V'cwxmui end-TertiaryuuirTum: u agemix"in the9::1"~'1'1':L111u,‘;_;\1north and east. ‘, . ,~ ,‘.‘. The area is made ‘.‘up mainly11.1’ of highly metamorphosed.«L and granitized sedimentary rocks of the Basement System of-East Africa. -It includes calcareous, semi-calcareous,VQHZ pelitic, semi-peliticg .,.r"\,*and psammiticnw'T'V‘MLL‘ types.Mp In the east the‘r: metamorphicIzm‘mmmplm' numbrocks have1mm twcwbeen invadedExxudcd Ia}by small ultra-basic‘,'.fl1iji\t\l£ plugs.“Myra, DetailsHum 4‘:are givenIn": ofw the petrology,[NUTKUWIAV‘VJA‘ petrography,wwwpna u"?and {Q‘VIMVH‘Leconomic minerals of the rocks and of the water-supply of the area. -~ GEOLOGY OF THE MWINGI\lWlXGi AREA.-\RE.\ I-INTRODUCTIONI --l\'I'R()l)L( H()\ The1‘1; \_'\‘1!i'l‘country" describedL‘VQ‘CL‘L‘L in this report is quarter-degree sheet 45 S.W. (Kenya), bounded "\_\by latitudes“ind-b 1? ° 00' S. and 0° 30' S. and by longitudes 38° 00' E. and 38° 30' E. It has an area ofm- aboutghoul 1,200 square miles and lies in the northern portion of the Kitui district of the Southern Province of Kenya, forming part of the Kamba native reserve. Itl'. isw inhabitedHinfzmm byh) about.L'PML'. 30,000Ftwm Wakamba“ukunitm who_‘ subsistmiww byPg. theMic cultivationg 1L.‘_.m‘1. of maize, beansE‘CLIIMKHQi]1i!:CL._\IILtI").and millet, and by herdinghurdm; cattlec.1L11c.-.miand goats.gym. At\! Nguni\"LHH «~11on the1.1m £1.=1'i~\._w.v-“Garissa road there is a camp(“min founded1‘“q by1.. E.y!"G.' Powellp_w L‘j' but“‘_.'. -subsequently.. 1 ‘_ ' acquired." _.,‘' i by1‘. TulaI‘m: Products1), . Ltd., a sub- sidiary of Diadem Products Ltd., where 'gypsum from the Tula valley, near Garissa, is processed for the manufacture of plaster of paris, chalks and whitening blocks. Powell also collected from the roots of certain thorn trees a vegetable' fibre'Whicll be ..baled and sold under the name "flotite" as an insulator, and originally as a substitute for ktttm\ 111life belts. Mwingi is theit‘c mainimm‘. villagewit and hascm.1Pna postfiur‘office,flgun{tuir'kwwmik'a market and Indian-owned1‘ J. HL‘L“ \f‘vL-l"shops, and. is1‘ theU'c scenewax”- ofm“ cattlewith auctions..L'nmnx. Itf'. lies1 on‘11. the11:: Garissa-Nairobi(.mzwu. \uw'fi road, which runs:_:vn. acrossn'nxx the1" southern~\‘-.il'.‘.:_"V portionDu: um of the area and forms\ the1h“ mainnun lineHTL' ofm' communication0‘W'.IT.'1\..LM" '.Hto the50 railway.. at Thika,l'ililxu. 80\‘U miles{1111l J.away. A railway{mu} wasWm plannedPiummd duringAw" ' the[11: 1939-1945NF“; IV-li war‘mu' toIn runWC.“through U"Gai toLL‘ theL": Northern\L=I"."1L Province.xcc hmbut the projectrmiicg‘. wasum abandonedV‘mtwdmwcfi when"$1193? NH;only the1%- ~11'xsurveying and grading of‘Hthefic rail-bed[ml-"Jed hashm beenNu!" carriedcm m1 outUNI asm farJ'L-J asm the111C Mwingi-Katze\Iw» ‘ g1 "L" road.Imus. BesidesBows.» the' Nairobi-GarissaCumin” road,zumi'. which\w‘H‘ is\\ maintainedHZLLH'HSHWL‘C byh} the PublicI’ut‘iu: \\\.“}\wWorks Department,qu'fl 117. therethat isix .=a good system" of Local Native-; Council(mu-13‘. roadsHuck thatH141 .tr'a‘are usableLmihlc duringduhng theHm dryin weather,“.czgmct'. but3511’. become difficult during the rains. RainR1: H fallsmm inm theHTC area“[111{:7mummm:xmxm‘x.in two distinct seasons, from(mm March\Im‘ch toIn May,Mn}. and.md. mmduring‘ ' November\mctnhu and«1U December.”camber. The"1 HQ rain,mm. whichux'mu'n falls“Mk mainlynumb in'H the evening,waning.