White clays

15
THE "VALENCIA WHITE" CLAY AN ASSURED RAW MATERIAL FOR CERAMICS
BY K M W Marshall*
(NIHERST)**

Acknowledgements
This article is extracted from a paper prepared for presentation to the Second Seminar on the Quarrying and Earth-Extractive
Industry in Trinidad and Tobago: Focus on Industrial Minerals,
due to be held on 3 April 1991
Acknowledgement is made of the kind permission of Ceramic (Trinidad) Limited, 68 Diamond Vale Industrial Estate, Diego Martin and Rotoplastics Limited, Bhagoutie Trace, San Juan, to quote from the results of investigations undertaken on their behalf.
** Written and submitted in a personal and private capacity, with permission of the President of NIHERST.

1. INTRODUCTION
The occurrence of modest resources of "White-firing non-ball clay" in the Pleistocene terraces of the WaIler Field-Valencia-Matura district gives the assurance that an indigenous raw material of known properties and characteristics, answering to this description, is available to the local ceramic industry. This article summarises the results of documented research, from the 1960's to the present, on the 'Valencia White Clay" or "white clay" - as it will be referred to herein. The white clay is of low-to-medium plasticity and is refractory when fired. It needs to be distinguished from gray clays high in plasticity, firing pink and buff, which also occur within the predominant gravel and sand lithology, Experiments on the formulation of a white-firing pottery body, suitable for both casting and jollying have been undertaken (references 5 and 6).
More recently, its potential for use in producing a pink firing ceramic title, in combination with the plastic (and normally red-firing) Talparo Formation clays, has been noted. Given the projected scale of ceramic production over the next decade, exclusive of structural clay products (clay blocks), what would appear to be economic reserves are known to occur on the Quare River, and at localities in Turure, Tattoo Trace, Tapana Road and on the North Oropouche River south of the Valencia Road.

2. GEOLOGY OF DEPOSITS
The deposits described are located in the Ward of Manzanilla, county of St. Andrew and found on State Lands forming the Valencia Forest Reserve and Wildlife Sanctuary, as well as on adjoining private lands. In the UTM system of mapping for Trinidad they fall within sheet 25 (1: 25000 scale). The white clay occurs in lenticular bodies of varying size, generally near surface or at very shallow depths -discontinuous strata of variable extent - in the alluvial tan deposits of the Cedros Formation (Kugler 1959), where they overlie sand and gravel deposits as well as other clay deposits of different lithology. The environment of deposition is typically alluvial and fluvatile, all of the terrace clay deposits being of secondary (transported) origin. However, the author holds that the white clay deposits may well be the product of soil-forming processes and proposes a similar origin for the economically important high-silica sands of the Matura and Melajo Forest Reserves. Both the white clay and high-silica sand are associated with the development of the terrace soils No.55: Piarco Series and No.255: Valencia Series, the latter having been described by Chenery (1952) as his 'best example of a tropical ground water podsol" (Brown and BaIly, 1970. The Cedros Formation, which is of Pleistocene age, unconformably overlies the Melajo clay member of the Springvale Formation of Pliocene age. The Melajo clay differs significantly from the white clay in mineralogical and chemical composition, and physical characteristics. The terrace deposits of the Cedros Formation at Valencia are the major source of naturally occurring gravel and sand in Northern Trinidad, and together with similar deposits at WaIler Field, Guanapo, and Matura, have been widely exploited for construction aggregates, as well as glass sands.
The white clays of Wailer Field, Valencia and Matura have long attracted the attention of both craft potters and industrial ceramics producers in their quest for an indigenous source of white or light-firing clay.
Recorded field and laboratory investigations undertaken in the 1970's included:

i) Chemical analysis of white clays by CARlRI (project code: E-CTA-73-1 -1: dated 7 May 1973) from surface and auger-hole samples taken by Ministry of Petroleum and Mines at localities in Wailer Field (Lalla's Quarry; Frank Kerry and Johnston: West Aripo River). The white clays generally have low iron oxide (Fe₂O₃) values of about 3 per cent or less. They we re subsequently sampled and tested under the CARIRI-Research and Productivity Council of New Brunswick (RPC) programme (reference 3)

ii) Under the CARIRI-RPC testing programme samples of white clay from Valencia were subjected to analyses and ceramic testing, as well as used in body formulation for use by the Les Lilas pottery at Chickland.
The results are reported in references 4, 5 and 6.

iii) Ceramic testing and evaluation (reference 8) by CARIRI of samples taken from the Quare River, Valencia "White clay" prospect. This deposit had been volumetrically surveyed (reference 7) by the Ministry of Petroleum and Mines, on the presumption that it was of homogeneous ·'White clay". This did not prove to be the case, the white clay comprising about five (5) per cent of total measured reserves of 1.5 million tons (long). However, this work was most useful in that it gives an indication of the individual bodies of white clay.
"'Turure" and "Cumuto Road" (precise localities not known) by a representative of International Pipe and Ceramics Corp of New Jersey in 1962 mineralogical and chemical composition consistent with those of the white clay (reference 2, page C vi-vii). Particle size distribution analyses were also performed.

4. EVALUATION OF TEST RESULTS
The white clay from Tattoo Trace and Tapana Road sand-and-gravel pits is from the same geological succession (terrace deposits of the Cedros Formation) as samples previously taken at locations in Waller Field and Valencia and generally display the same ceramic properties (reference 3,4,5,6,8 and 10).
The mineralogical and chemical analyses of the white clay from Tattoo Trace and Tapana Road are set out in Tables 1 and2 together with those for representatives samples from the work on Wailer Field and Quare River (Valencia) clays reported by Barnet and Osborne (reference 4) and Phillips- CARIRI (reference 8). Analyses of a plastic clay sample from the Melajo member (Springvale Formation) of Pliocene age which underlies the terrace deposits have been included for purposes of comparison (reference 2, Page C xiv-xiv). The results obtained from the Tattoo Trace and Tapana Road samples (CTP/37 &RFCIO1) are similar to those for white clay from Quare River in Valencia and the Lalla Quarry in Waller Field, for example.
The distinguishing feature of the white clay is the low iron (Fe2O3) content and the almost total absence of clay minerals of the montmorillonite group, which are expansive or "swelling" minerals and impart plasticity to clay bodies.
The unfired and fired characteristics Sampling and analysis of clays from of the white clay are summarised in Table 3. Here the distinguishing features are shown to the low drying-shrinkage, low plasticity, high water absorption, low but adequate strength and light fired colour.
The particle -size distribution reported for the white clay at Tattoo Trace shows it is to be of medium fineness, thus displaying a very close distribution to that of the 'Talparo Clay" (Caparo clay member of Talparo Formation - Kugler 1959) at a locality on the lands of Caroni (1975) Limited (reference 8, page 25). Of the material passing the 200-mesh sieve, six (6) per cent was fine sand, thirty four (34) per cent silt, and sixty (60) per cent clay (less than 0.002mm). The only other particle -size analysis available for the Pleistocene beds at Valencia is from an unspecified locality at Turure (reference 2, page C vii) and shows a very sandy silty clay.

5.ECONOMIC POTENTIAL OF MATERIAL
The white clay has application in the following areas of manufacture: ceramic goods and materials i.e. bodies which are fired at high temperature in the course of production, and as a filler or extender in paints, coatings, adhesives, inks, cosmetics, plastics and paper among others. The white clay should be processed to reduce silt, and remove sand and the water-soluble salts that may be present, and generally improve the quality of the material.
In the area of ceramic goods and materials, the white clay should find a ready market in the existing pottery and earthenware industry. Indeed, this section of the local ceramic industry has been clamouring for dependable and local supplies of light or white-firing clay. Now that the economic geology of the Pleistocene white clay has been outlined, it should be possible to supply this market. lt must be emphasised however, that ceramic bodies for firing are usually composed of several plastic (clay) and non-plastic (e.g.. Silica sand) ingredients, and that white clay will most probably be mixed with one or more varieties of plastic clay, either of local or foreign origin. Such bodies may Include stoneware, as well as sanitary ware, either of the vitreous or earthenware variety.
It is perhaps in the production of ceramic floor and wall tiles that the greatest potential for the utilisation of the white clay exists.

INFERRED RESERVES - QUARE RIVER DEPOSIT
Given the results of volumetric survey carried out the Quare River to the west of the Tattoo Trace sample location (references 7 and 8) and of ceramic tasting (Phillips - CARIRI in reference 8) a white clay deposit over an area of approximately 2.6 acres (1.05 hectares), with a maximum thickness of three (3) meters, may be outlined. For a gross volume of 31,680 cubic meters, using a measured unit weight of 1738 kg/m3 for the white clay, a gross mass of 55,000 tonnes is indicated. (Such reserves would be inferred under the USBuMinlUSGS classification of 1976). Deducting a one-half allowance for discontinuities and unsuitable material a net volume of 28,000 tonnes can be taken as exploitable material. At this point it is well to recall that the deposits of white clay consists of relatively small, scattered, irregular and discontinuous lenses and beds of material.

REFERENCES CITED
1.1959 KUGLER, H G (compiler) Geological map (and sections) of Trinidad - 1:100 000 (1959) Petroleum Association of Trinidad

2.1968 MARSHALL, K M W (Compiler) Analyses of Trinidad & Tobago rocks, minerals and ores Geological Section, Ministry of Petroleum & Mines, Trinidad & Tobago October 1966

3.1970 BROWN, C B and BALLY, G S Soils of Central Trinidad - Land Capability Survey of Trinidad and Tobago No.4: Government Printery, Trinidad & Tobago, 1970.

4.1974 BARNETT, D E and OSBORNE, R WA Evaluation of possible ceramic materials from Trinidad Report M175/47. Research and Productivity Council, Fredericton, New Brunswick, Canada. June 1974

6.1975 BARNETT, D E and PHILLIPS, E M Transfer of ceramic technology - May 12-June 27, 1975. Report M/75/77, Research and Productivity Council, Fredericton, New Brunswick, Canada. July 1975.

7.1976 ALEXANDER, C Clay resource evaluation in Trinidad and Tobago Phase 1 - Field Survey Geological Section Ministry of petroleum & Mines Trinidad and Tobago. 1976

8.1977 PHILLIPS, E M - Caribbean Industrial Research Institute (CARIRI) Ceramic evaluation of clay deposit at Quare River - Valencia. Clay resource evaluation project E-RE74-30-1. St. Augustine, Trinidad. March 1977

9.1987 MARSHALL, K M W - Consulting Geologist Caroni (1975) Ltd, Brechin Castle,
Couva, June 1987 (PRIVATE & PROPRIETARY REPORT)

10.1989 MARSHALL, K M W - Consulting Geologist Report on clay sampling: Bescrete,
Tattoo Trace and National Quarries, Turue - Valencia. Ceramic (Trinidad) Ltd, 6B Diamond Vale Industrial Estate, Diego Martin. 1989

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