312 



DEPARTMENT OF THE INTERIOR 



Table XVIII. 



2 GEORGE V, A. 1912 



- 



1. 



Augite min- 

 ette (No. 900). 



2. 



Hornblende- 



augite minette 



(No. 493). 



3. 



Olivine-augite 



minette 



(No. 836). 



4. 



Mean of 

 1, 2 and 3. 



5. 



World - 

 average min- 

 ette. 



SiO., 



53 32 



SO 



14 16 



215 



508 



10 



790 



7 12 



05 



12 



239 



4 80 



■26 



124 



■66 



53-68 



•90 



16 89 



1-28 



5-53 



11 



370 



6 -08 



10 



•38 



403 



4 32 



10 



185 



105 



48 



12 

 1 

 5 



9 



8 



1 

 4 



2 



2 



23 

 81 

 56 

 87 

 26 

 13 

 07 

 94 

 05 

 24 

 81 

 67 

 97 

 63 

 78 

 64 



51 



14 

 1 

 5 



6 



7 



2 

 4 



1 



78 



87 



54 



77 



29 



11 



89 



35 



07 



25 



74 



60 



44 \ 



91/ 



83 



88 



49 45 



Ti0 2 



Al a O, 



Fe 2 



1-23 



14 41 



3 39 



FeO " 



MnO 



MgO 



CaO 



SrO 



BaO 



5 01 

 13 



8 26 



6 73 



Na„0 



KoO 



2 54 

 469 



H 2 0- 



H„0+ 



P.0 8 



co 2 



2 43 



1 12 

 ■61 

















100 25 



100 00 



100 76 



100 32 



100 00 



Considering the relatively great amount of alteration suffered by all these 

 rocks the correspondence of the two averages is quite close. This essential 

 equivalence of chemical types points clearly to the prevalence of a general law 

 which underlies the generation of these lamprophyres wherever found. It 

 should be noted that the world- average includes analyses of minettes that are 

 mineralogically transitional to the kersantites. The analysis of the hornblende- 

 augite minette (No. 493) corresponds to a similar transitional type. 



Kersantite. — The long band of Pend D'Oreille limestone running from 

 Lost creek to Sheep creek, parallel to Salmon river and two miles distant from 

 it, is traversed by dikes of mioa-lamprophyre. Two of these, each about four 

 feet wide, crop out on the summit of the ridge dividing the waters of the two 

 creeks. Petrographically, they are similar to other dikes, occurring along the 

 Pend D'Oreille river. All of them are altered in varying degree, so that the 

 microscopic diagnosis of these lamprophyres is difficult. For this reason, one 

 (four feet wide) of the two dikes cutting the limestone, the freshest of all 

 those encountered in ~the different traverses, has been selected for chemical 

 analysis. 



The rock is a dark, greenish-gray, fine-grained, non-porphyritic trap, 

 evidently highly micaceous. Under the microscope it is seen to be essentially 

 a panidi amorphic aggregate of brown biotite and an imperfectly twinned 

 plagiocla-e. A little orthoclase is almost certainly present. Magnetite and 



