BASELINE GEOCHEMISTRY OF DEVONIAN AND CARBONIFEROUS

METASEDIMENTARY ROCKS IN CORNWALL

N.G. LeBoutillier, P.W. Scott, R.K.Shail and R.C. Scrivener

•468 samples of metasedimentary rock were taken from a variety of coastal, inland, quarry and temporary exposures across Cornwall.

•Samples had to be free of any visible effects of weathering and/or mineralisation of any kind.

•The samples were crushed and milled to a fine powder and shipped to Vancouver where they were analysed by ICP-MS, following a four-acid digest, for a suite of 40 elements (+ gold).

•The resulting database holds over 19,000 records and in conjunction with its associated GIS, geographical and geological databases, forms an important resource which has applications across a wide variety of fields.

Original map courtesy of Dr Brian Leveridge (unpublished)

THE PROJECT DATABASE HOLDS A TOTAL OF 468 METASEDIMENT SAMPLE RECORDS.

OF THESE:-

• 279 ARE FROM THE GRAMSCATHO BASIN

• 74 ARE FROM THE LOOE BASIN

• 67 ARE FROM THE SOUTH DEVON BASIN

• 35 ARE FROM THE TAVY BASIN

• 13 ARE FROM THE CULM BASIN

THESE METASEDIMENTS HAVE BEEN BROADLY CLASSIFIED BY LITHOLOGY INTO MUDSTONES, SILTSTONES AND SANDSTONES. THE DATABASE HOLDS THE RECORDS OF:-

• 285 MUDSTONES

• 48 SILTSTONES

• 135 SANDSTONES

M o_ppm Cu_ppm Pb_ppm Zn_ppm Ag_ppm Ni_ppm Co_ppm M n_ppm Fe_% As_ppmAVER 0.51 32 19 106 0.1 53 24 871 4.74 23

MEDIAN 0.4 26.2 13.6 98 0.1 53.9 23 670.5 4.82 14MODE 0.2 22.2 13.7 97 0.1 29.9 24 665 4.72 7

ST DEV 0.5 24 23 50 0.1 21 10 702 1.39 25

U_ppm Th_ppm Sr_ppm Cd_ppm Sb_ppm Bi_ppm V_ppm Ca_% P_% La_ppmAVER 2 8 88 0.13 1.5 0.27 124 0.44 0.05 24

MEDIAN 2.3 8.1 73 0.1 0.9 0.2 130 0.15 0.056 23.55MODE 2.3 7.6 52 0.1 0.5 0.1 147 0.04 0.056 20.3

ST DEV 0.64 3 57 0.12 2 0.21 40 0.86 0.03 10

Cr_ppm M g_% Ba_ppm Ti_% Al_% Na_% K_% W_ppm Zr_ppm Ce_ppmAVER 97 1.28 434 0.35 7.97 0.99 2.49 37 90 52

MEDIAN 98.5 1.23 438 0.32 7.92 0.64 2.65 26.1 93.6 51MODE 124 1.32 463 0.27 6.19 0.47 2.19 0.6 113.3 48

ST DEV 33 0.52 175 0.14 2.01 0.88 1.08 37 27 20

Sn_ppm Y_ppm Nb_ppm Ta_ppm Be_ppm Sc_ppm Li_ppm S_% Rb_ppm Hf_ppmAVER 4 12 8 0.59 2 13 109 0.09 111 3

MEDIAN 2.8 10.6 7.1 0.5 2 13 99.9 0.05 102.5 3.1MODE 2.9 9.5 5.7 0.5 3 11 53.2 0.05 61 3.5

ST DEV 6 6 4 0.24 1 4 59 0.08 55 0.85

•Analysis of the data to date has yielded important information on the background chemistry of the metasediments in Cornwall.

•It has direct application to the study of metasediment mineralogy and provenance.

•It can be used to characterise particular formations as an aid to ‘geochemical mapping’.

•It is an important resource for those studying metal transport within the soil and into the biosphere.

•It is an important resource for those bodies dealing with hydrological modelling and the definition of what constitutes pollution.

Acknowledgements:

•Funding from the European Social Fund (Project No: 011019SW1).

•Dr Brian Leveridge.

•BGS Keyworth

•Mr Steve Pendray (Camborne School of Mines).