3/31/2015

Thoughts on the Beaverhead Impact Crater Morphology:

Based on information gleaned from studying oil and gas exploration well logs and reports in Idaho, Oregon and Washington, outcrops in Montana and Idaho, and remote sensing using Google earth and USGS Geologic Units in the following States: Idaho, Oregon, Montana and WashingtonTim McElvain

Legend

Beaverhead Impact Crater Rim: based on outcrop and well data and my interpretation of the surface exposureof the Idaho Batholith

Truncated top of Central UpliftCrater Rim 2015 GoogleData SIO, NOAA, U.S. Navy, NGA, GEBCOData SIO, NOAA, U.S. Navy, NGA, GEBCOImage Landsat200 miKi; Ki?; Kif; Kii; mig; Y?s: Intrusive rocks: mostly Late Cretaceous granodioritic to granitic plutons of the Idaho batholitic assemblage, but including some Eocene intrusions; northern Idaho and Atlanta batholith (Cretaceous to Eocene) [ Mesozoic Cenozoic ] Cretaceous-Late Tertiary)

Image Landsat

Beaverhead Impact Crater Rim:based on outcrop and well data and geological quadrangle maps, My interpretation of the surface exposure of the Idaho Batholith

Beaverhead Impact Crater Outlined on a Google Earth Map Print exhibiting the following formations: Ki; Ki?; Kif; Kii; mig; Y?s: Intrusive rocks: mostly Late Cretaceous granodioritic to granitic plutons of the Idahobatholitic assemblage, but including some Eocene intrusions; northern Idaho and Atlanta batholith (Cretaceousto Eocene) [ Mesozoic Cenozoic ] Cretaceous- Late Tertiary)

I have outlined my interpretation of the Beaverhead Impact Crater based on my study of oil and gas drilling logs and reports in Idaho, Oregon and Washington, along with the outcrop at the eastern edge of the crater, and remote sensing. The large circle represents the edge of the crater and the small circle in the center represents the outcrop of the truncated central uplift.I believe the Idaho Batholith represents the basement rock brought to the surface by the rise of the central uplift, which was sheared off by large thrust sheets.With respect to thrusting, over thrusting, overthrust sheets: in the Cascadia subduction zone thrust sheets have piled up mountain ranges in the northern Rocky Mountains from Wyoming to British Columbia. These mountain ranges are structurally very complex but fairly well understood as a result of oil and gas exploration wells throughout the zone. It could it be possible that some of the big overthrust sheets traveling north and northeast sheared off

the top of the central uplift and pushed it northward into the crater and over the crater rim to the north and east. The remnants of the uplift, represented by the Idaho Batholith outcrops, were then dropped from the thrust sheet to the north and northwest of the crater. If this is true than I would not expect these allochthonous blocks of granite to be rooted. It seems to me that the large thrust sheets could be compared to the bulldozing effect of advances and retreats of continental glaciation and the mountain ranges could be compared to terminal moraines.One might then wonder if the Neoproterozoic Conglomerate and Breccia in the Formation of Leaton Gulch, Grouse Peak, and northern Lost River Range, Idaho has any relation to the Beaverhead Impact Structure. These rocks may be allochthonous blocks that have traveled a great distance and might be related to a Neoproterozoic Impact Structure that happened at another time and another place.

The idea that the central uplift has been sheared off is a radical idea but I suggest the following to test it:

Generally speaking the Supergroup and younger formations within the thrust sheets generated by the Cascadia Subduction Zone are not metamorphosed or if so they are metamorphosed at a very low level. The Belt Supergroup and younger formations in the Allochtons south and west of the Central Uplift are marginally metamorphosed if at all. These formations exposed on and around the central uplift vary in metamorphism some are highly metamorphosed but most are marginally if at all. The most of the formations in the Thrust Klippe to the north of the Central Up lift are highly metamorphosed. There is a question if this metamorphism is regional or shock metamorphism. However; as one moves north the percentage of highly metamorphosed rock diminishes until one reaches the Coeur DAlene

Quadrangle there are only isolated patches of highly metamorphosed rock.(See: Geologic Map of the Central and Lower Big Creek Drainage, Central Idaho; Preliminary geologic map of the Elk City region, Idaho County, Idaho; Geologic Map of the Idaho Parts of the Orofino and Clarkston 30 x 60 Minute Quadrangles, Idaho; Geologic Map of the Kooskia 30 x 60 Minute Quadrangle, Idaho; Geologic map compilation of the Hamilton 30 x 60 minute quadrangle, Idaho; Geologic Map of the Potlatch 30 x 60 Minute Quadrangle, Idaho; Geologic Map of the Headquarters 30 x 60 Minute Quadrangle, Idaho; Geologic map compilation of the Missoula West 30 x 60 minute quadrangle, Idaho; Geologic map of the St. Maries 30 x 60 minute quadrangle, Idaho; Geologic map of the Coeur d'Alene 30 x 60 minute quadrangle, Idaho)To my knowledge the thrust sheets generated by the Cascadia Subduction Zone throughout

the Northern Rocky Mountains did not generate enough heat and pressure to cause regional metamorphism. The most highly metamorphosed rock in this entire zone is immediately north of the proposed central uplift of the Beaverhead Impact Crater. The heat and pressure generated by the Beaverhead bolide impact would have created enough heat and pressure to metamorphose rocks over a rather large area; however, the metamorphism would probably be more akin to shock metamorphism than to regional metamorphism. I believe thatit would be interesting to study these rocks and try to determine if the Belt Supergroup and younger formations in this area were shock or regionally metamorphosed

Topographic Map of the Beaverhead Impact Crater:small circle Outcrop of the top of the truncated Central Uplift, and two cross sections from well logs, and one modied fromArney et. al 1984

A

A

C C

BB

Meyers Fed No 1Hagenbarth No 22-25MilfordFederal 19-1Cook No 26-1Idaho State No 1AA

Beaverhead and Tendoy mountains a stack of multiple thrust sheets composed of rocks ranging in age from Precambrian through Cretaceous pushed into crater

Triassic

Pp

Sea Level

-500 meters

Crater ll - Volcanics and sediment??

Tkb??

Kbl

Precambrian

?-1000 meters

Tuff

??Tkb Formation thinning as the crater oor rises to the central uplift

-1500 metersPp

Kjke

Cretaceous

-2500 meters

-3000 meters

-3500 meters

Jm

?Pp

Precambrian

?

Possible crater oor if Milford TD is in Volcanics Possible Crater oor if Milford TD 1s in Precambrian

After studying logs and reports of other wells drilled within what I believe is morphological Beaverhead Crater;I am very suspicious that the Milford well landed in at or near the Precambrian or crater oor . I believe the operator stopped drilling thinking they were close to drilling into the Precambrian and that they would not encounter any Cretaceous or older shelf formations if they drilled deeper.

I feel justied placing the Beaverhead and Tendoy Mountains on top of the Beaverhead conglomerate in the cross section after visiting the outcrop and seeing Tendoy mountains on top of the Beaverhead formation in Big Sheep Canyon.

BBCross Section B - B: 1950-01: Juniper No. 1 well to the Blue Mountain No, 1 well

Sea LevelB- 5000 ftPrecambrian ??The edge of the crater shouldbe somewhere in this area.BPrecambrian ? (see below)TD in Mm??-10,000 ft???

The 1950-01 : Juniper No. 1 Well Logs indicate that the only formations the well penetrated were Paleozoic limestone; however I believe the limestone penetrated by this well is a part of a thrust sheet and therefor does not necessarily indicate that the well is located outside the crater rim.Bostic 1-A well - The operator and well site geologist believed the well bottomed in granite-wash or Precambrian, but there is another interpretation please see the report below which can be found in the Bostic Well folder le PDF Name -1972-03-reports.pdf.The authors believe that the silicic rocks at the bottom of the well are not just above the Idaho Batholith or other Precambrian igneous rocks. They think the Precambrian is much deeper. This is a good report with a schematic a cross section from the Bostic well north (toward the central uplift?) that ts my Interpretation of the crater morphology.The Standard of California - Blue Mountain Unit No 1, on the western end of the cross section bottomed in black diorite. In the well notes and reports this formation is sometimes referred to as volcanic and other times as Precambrian. I do not believe that any of the wells drilled in this quadrant of the Beaverhead Impact Structure penetrated the Precambrian or any formation older than the Tertiary.

Cross Section C - Cfrom Bostic 1 A Well north to Mount Bennett Hills modied after Arney et.al. 1984

CC- 5

LA-9966-HDR

Los Alamos National Laboratory Is operated by the University of Callfornla for the United States Department of Energy under contract W-7405-ENG-38.

Petrographic Analysis and Correlation of Volcanic Rocks in Bostic 1-A Well near Mountain Home, Idaho

[L'CJ fi}. nrn'Rl'CJ.LosAlamos National LaboratoryU@u U uLosAlamos,New Mexico 87545

An AffurnaUve Action/Equal Opportunity Employer

This work was supported by the US Department of Energy, Division of Geothermal and Hydropower Technologies.

Edited by Glenda Ponder, ESS Division

DISCLAIMER

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied , or assumes any legal liability or responsibility for the accwacy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation , or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

LA-9966-HDR

UC-66aIssued:January 1984

Petrographic Analysis and Correlation of Volcanic Rocks in Bostic 1-A Well near Mountain Home, Idaho

Barbara H. Arney Jamie N. GardnerStephen G. Belluomini*

*Harding-Lawson Associates, 7655 Redwood Boulevard, P.0. Box 578, Novato, CA 94947.

[Lrry@ nfnmrc)' Los Alamos National LaboratoryU@u Li uLos Alamos,New Mexico 87545

PETROGRAPHIC ANALYSIS AND COR RELAT ION OF VOLCAN IC ROC KS I N BOSTIC 1-A WELL N EAR MOUNTA I N HOME , IDAHO

byBa rbara H . Arney , J ami e N . Ga rdner , and Stephen G . Bel l uomi n i

ABSTR ACT

De ta il ed exami na tion of volca nic rock cu tti ngs from the Bosti c 1-A well nea r Moun tai n Home , I daho , prov i des data tha t correl a te the strati graphy of the wel l wi th the reg ional strati g raphy of the we stern Snake Ri ver P l a i n . The Bosti c 1-A wel l penetra tes basal t of the Mi ddl e Pl ei stocene Br u neau Forma tion and u nder ly i ng sedime n ta ry rocks of the U pper P l iocene Gl en n s Fer ry Formati on . Ba salt u n d erl y i n g the G l en n s Ferry Forma tion i s most l i kely Ba nbu ry Ba sal t of Mi ddl e P l i ocene age or Ba nbury equ i val ent . A 350-f t i n terva l of fel sic vol can ics i s then i n tersected above another 600 f t of ba salt . The wel l bottoms i n a l tered fel sic vol cani cs .The l owe st 600 f t of ba sal t fl ow s has not been correl ated withany basal t observed on the su rf ace . From the establ i shed strati graphy of the reg ion , and from petrogra ph ic ev idence , the sil i cic volca n ic roc ks occu rri ng both above and bel ow the l owermost basa l ts i n the wel l a re proba bl y l ower P l iocene I davada Volcani cs . No rth of the well , i n the Mt . Ben nett H i ll s, ldavad a Volca ni cs overl i e crystall i ne rock s of the I daho ba thol i th . No estima te of depth to pl u ton i c bed roc k can be ma de from the wel 1 da ta al one. Strati graphic compa r i son s sugge st a s l ittl e a s 0 .2 to 0 .3 km more of I d avada l i e benea th the Bosti c 1-A wel 1. Resul ts of geophysi cal studi es sugge st additional ba salt 1i es benea th the Bosti c 1-A rather tha n gran i tic rock s of the ba thol i th .

I .I NTRODU CTI ONThe Bosti c 1-A well , on the northe r n ma rgi n of the Sn a k e R i ver P l ai n near Mou n tai n Home , I da ho (T4S , R8E , S25) ( Fi g . 1) was dri lled as an oil and gas wil dcat to 2950 m ( 9676 f t ) by Al Grif f ith i n 1973. I n 1974 Gu lf M1nera l Resou rces Co. took over the well as a geothermal prospect and ran addi ti ona l l ithol og i c and geophy sical l ogs . I n earl y 1978 the well wa s acqui red by U n ion Oil Co., who attempted to cl ean i t ou t, then pl ugged a nd aba ndoned i t i n October 1978.

W hen the area ea st of Moun ta in Home , Idaho , wa s sel ected f or study as a poten ti al hot dry roc k ( HOR ) geotherma l site ( A rney et al. 1982 ) , a study of the Bosti c 1-A cutti ngs was begu n . The study reveal ed tha t the well i n fact bot tomed i n sil icic vol can ics of the I davada Forma ti on rather than gra n i te a s prev iou sly reported ( Gu lf Mi neral Resou rces Co ., l i thol ogic l og ) . Bel iev i ng that I daho Ba thol i th l ay benea th the sil icic vol can ics , as i ndeed i t does j ust nor th of the HOR prospec t ( Mal de et al . 1963) , we studied , i n more deta i l , the volca n ic strati graphy i n the well to estima te the depth to g ran i te . The resu l ts of that work are presen ted in th i s report .Subseq uen t grav i ty model ing suggests that no granite l i es benea th the sil icic volca n ics at the Bosti c l oca ti on . I n stead , rock s benea th the bottomof the Bosti c 1-A wel l a re i n terpreted to be ba sal ts ap proxi ma tely 3 km th i ck , p roba bl y assoc i a ted wi th the open i ng of the Snake R i ver P l a i n ( Arney et al . 1982) .

I I . PROCEDU RESWell cu tti ng s we re exami ned wi th a bi nocul ar mi croscope ( Ap pend ix A ) . Sampl es were taken at 9-m ( 30-f t ) i n terva l s f rom depths of 426 to 536 m ( 1405 to 1769 f t ) , an d at 3-m 00-f t ) i n terval s from 1219 to 2949 m ( 4023 to 9676 f t) . The small si ze of the well cu tti ngs and thei r f i ne grai n size h indered mi nera l iden ti f ica tion i n some sampl es . Cu tti ng s bel ow 1768 m ( 5800 f t ) were mo u n ted on poster boa rd ( Fi g . 2 ) at 0.5 i n . = 10 f t to al l ow a better u n d er- stand ing of the l ower vol can ic sequence . Deta i l ed petrog raph ic study was perf ormed onl y on cu tti ngs of the vol can i c rock u n i ts. G ra i n mou n ts prepa red of sampl es f rom depth s be tween 1239 and 2949 m (4090 to 9676 f t ) were exami ned w i th a petrog raphi c m icroscope to i den tif y formation and rock types ( Ap pend i x B ) To ai d i n correl ati on wi th ma p ped surf ace un i ts of the Idavada Vol can ics , represen tati ve in terval s f rom each v i sual ly di stinct sil icic u n i t i n the cutti ngs were chemi ca lly anal yzed usi ng x- ray fl uorescence ( X RF ) , foll owi ng the method of Haga n ( 1982 ) . C u ttings from these i n terva 1s were hand-pi eked , and th i n secti ons made f rom the ha nd-picked sampl es we re exami ned pe tro graphi cal l y .To identi fy the alterati on mi nera l s presen t , sel ected sampl es were al so anal yzed by x- ray dif fraction ( X RD ) on 400 mesh powder s. When pea ks of the a l teration mi neral s were obsc u red by the ori g i nal mi neral ogy , an addi ti onal

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