MINEBK00378

• County: Gilpin
• Volume: 6
• Document: Inspectr
• Suffix: D

.GEOLOGY.
The only geological...eurvoy of the district is a partial one,containad in the
th a ~!poologicah 1':xpl,oration of.,the Fortieth Pnrallgl by Clarence ];irttf,(1II~0).
OO
non- T]ie csuntry~rocY.~may~be genorall.y•`doscribedas-a gneissicor ban
ded graniterhough
having sometimes a destinctly~graniti'c efiaracter.It frequently shows n thinly
~bsnded structure.
r;
Intrusions of quartz porphyry,~cotmnonly knmm ns porphyryraro to be found along the
' ` joint planot+;yrnich ,cross the gneiss. At ih is point such an intrusion is
quite not-
icable it•appearing nlong the surface atseveral points in close proximi~tyto.
wr.ch-. ,
the apex of tkie•'veiit„~whil'o on goi~n~'~edatit se'ems"to~take'a~'morcnorthorly
course going toviard Bob-tail Ilill. On the uthrlevel,v/oat of the main shaft it

forms the foot vrall of the north vein for oome distance. The matter of determining
., ice.,.
S.Oenator edletherthis intrusion hada-direct, influence on the ore deposition has not~been
!300000 taL•en up'to any extentr ~ ~ -
Tl:e lodesrypossess a high degree of'parallclism in their ntri1:e'or direction;
consisting their course vtith but four exceptions~bsing between due oast and neat on the one 9y
. whimrtaY,ing hand and north east and south L'1C3t on the other.
e above ~ The dip of the voins,.varyrchanging froquontly.vrith depth.
ftfto the The veins..dhotrrlittle.!indicatiori'of havingfdlled a,finnureras usually uriderntood,
Bich hnn con- but follovr the cleavage joints rand in eoms ~caees the Foliation plwios Hof the gneiss
and rspluco the country roc]-, on each side of them. The joints alsocrass the
porphyry dyke•and the veins are sometimes fowul in the lnttor rock.

Tha vrallo of the valna arc Naually viol! dofino~l. A thin clay selvage or parting
between the vialla and vein filling,in: apparont.;in mo~t~canes.

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