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and lhe second corresponding 10 a field in the composition of oligoclasc (An20· An30).
The firsl group falls inlo the field of plulonic. mewnorphic and authigenic feldspars, and
combining this informalion with information from cathode luminescence studies. it
undoubtedly incllXles some feldspars whkh have expc:rie~ low lI:mperarure aheralion;
however, no distinction is possibk: between (cldspan wlticb Iuovc been albilised in the
50Urce rock, anti those which wen: albilised in the presena: hosl rock.
The feldspars of the second group conlain very lillie polassium. and thus (hey fall
into the field of plagioclase feldspars with a metamorphic or plutonic provenance rather
thJn Ihost: with :II volcanic provenance. Thus the lack of zoning observed in plagioclase
feldspars illihis case ITa)' It1Wlly indicate deriyation from a plulOrUc or mewnorphk
Potassium feldspars conLtin signifJCaflt bul noI IIIte amounts of sodium and also
fall inlo the field of feldspars derived from a plulonic or metamorphic source. They also
typically coolain significant proponions of Ba. which is typical. according to Van de
Kamp and Leake (I98~) of k.(cldspars derived from a 'granitoid' source. A'Jthigenic
potassium feldspars are preset'l in one sample o( the Mainlan:I flX1lUltion. and these are
Yet)' pure onhoclase, plooina II the orthoclase pole.
4 2 3.5 SrdjlD(D!j1ry Rock FragID£Dls
Shale chips (types I and 2) are the dominant sedimenlary rock (ragment in all
lhree (ormations (plate 4.5). Dark. organic rich, well laminated shale chips are
pankularly abundant in the Goose Tickle group. Some of the dark sl'lale chips show