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Enders, Steve

From:Paulo Vasconcelos [

Sent:Friday, October 08, 1999 10:07 AM

To:Enders, Steve

Subject:RE: Received Morenci cryptomelane samples

Steve,

I crushed the samples last night and picked 13 grains from 288c and 8 grains from 288a. I will Fedex them to Australia today and the irradiation will leave from Australia next week. I will also send some of the left over grains in the next available BGC irradiation.

Paulo

-----Original Message-----

From:Paulo Vasconcelos [SMTP:

Sent:Thursday, October 07, 1999 2:38 PM

To:Enders, Steve

Subject:Received Morenci cryptomelane samples

Steve,

I received the samples and examined them. The sizes are suitable. 288a

and 288c are very good. 288b might yield some clean grains, but the

possibility of contamination is higher. I will prepare a and c if you are

happy with that decision.

Paulo

> >Paulo,

I will send you an overnight package tomorrow, so you should have

the samples on Thursday. The package will contain three samples ( #288a,

#288b, and #288c) taken within 50 meters of each other in the same zone.

I did preliminary XRD work on them; and although the peaks were not very

well defined, I tentatively identified cryptomelane and hollandite. I

sent them to Beatriz Vieira at CVRD’s lab in Belo Horizonte, Brazil for

confirmation. I’ve copied her comments and given you descriptions below:

”Comments: In this group, the #288b sample showed the best pattern in

graphic. There are 3 small peaks that fit very well in the pattern of a

Zinc Manganese Oxide - Zn2Mn3O8. I’m not sure if it’s possible in the

paragenesis, but the peaks were not explained by any one mineral. The

#288a sample presented the worst and most complex pattern, probably due

poorly crystalline minerals as you said. The same peaks of the “possible

Zinc Manganese Oxide” appear in this sample. Because the other

constituents have low crystallinity, the results suggest more quantities

of this mineral. It’s important to consider that the Majiorite peaks -

(NA,K)Mn8O16.xH2O are very coincident with the Cryptomelane and I can’t

affirm that this phase is absent in these samples.”

#288a Dark brown, 3-dimensional, spray of dendrites 0.5 mm in diameter

with metallic streak; Cryptomelane / Hollandite (63%); Zinc Manganese

Oxide (30%); Quartz (6%), Muscovite (trace)

#288b Dark brown, sponge-like texture; Quartz (57%); Cryptomelane (18%);

Microcline (13%); Zinc Manganese Oxide (11%), Muscovite (trace); and

probably trace of Hollandite and Hausmannite (Mn3O4).

#288c Dark brown, massive, 0.2 to 2 mm banded crustiform; Cryptomelane

(70-80%), Hollandite (20-30%), Todorokite (trace), Muscovite (trace).

I would think sample #288c is the best candidate, but I will send all

three for you to examine and choose. You should have enough sample

material; if not, please let me know, as I will have to make new separates

and overnight them to you. Please let me know what you think, after you

had a chance to look them over.

Cheers,

> Steve

-----Original Message-----

From:Paulo Vasconcelos [SMTP:

Sent:Tuesday, October 05, 1999 12:03 PM

To:Enders, Steve

Subject:RE: Morenci cryptomelane dating

Steve,

Please send the samples to:

Paulo Vasconcelos

Berkeley Geochronology Center

2455 Ridge Road

Berkeley, CA 94709

I am holding the UQ irradiation to include your samples in it. I will also

try to put the grains in the first available irradiation at the BGC.

Regards,

Paulo

Hi Paulo,

Thanks for the reply! I did think you had fallen off the planet,

but it is good to know you were just hiding down under it, so to speak!

> Yes, I would like to give this approach a try. Please send me the

best mailing address and I can get you a sample via overnight express yet

this week.

> I’ve finished my work on the mid-Tertiary to Recent volcanic and

sedimentary stratigraphy of the Clifton-Morenci area. Based on this work,

I’ve concluded that the copper oxide zone at Northwest Extension was

probably formed in the Pleistocene, perhaps since ~1 Ma as a result of 300

meters of down-cutting by the Gila River. A good date on my sample of

cryptomelane/hollandite would help substantiate or refute this

hypothesis!

> Thanks for your help with the earlier samples. I look forward to

working with you on this one.

Cheers,

> Steve

-----Original Message-----

From:Paulo Vasconcelos [SMTP:

Sent:Tuesday, October 05, 1999 9:37 AM

To:

Subject:Re: Morenci cryptomelane dating

Steve,

I sent you the message below, but you may not have received it.

Regards,

Paulo

Steve,

Strange way of getting in touch again. I am sorry for “having falling off

the edge of the planet”, but that is life in Australia. Despite loosing

touch, I did have the opportunity to run x-ray diffraction analyses on

Mn-oxide separates from the samples you sent me. I only identified

todorokite, birnessite, and pyrolusite. None of the separates analyzed

contained hollandite.

I am glad to hear that you have been able to identify and separate

cryptomelane in your samples. Paul Renne told me that he would not have

the time to run your samples but that I could use the equipment at the BGC

to analyze them. However, after talking to Tim Becker, the lab manager, it

does not look like they will be sending a suitable irradiation in the near

future. I have a 7-hour irradiation going out next week from Australia and

I could easily fit your samples in that irradiation. To make sure that you

get your results before December, what I would do is separate the grains

here at the BGC, send half of the grain separates to be included in the

irradiation being sent from Australia, and keep the other half here. If

the Berkeley guys send a suitable irradiation before the end of the year, I

will irradiate the other grains. This way we will be sure that your

samples will be run, either here or in Australia.

If you are interested, send me the cryptomelane sample as soon as possible.

The cost for running the samples here vary from U$600 - U$1000 per sample,

depending on the number of steps to be analyzed. In Brisbane, the costs

are A$1500 (~ U$ 970) per sample, and two to three grains will be analyzed

for the sample, depending on the reproducibility of the results.

Let me know if you want to proceed with the analysis.

Regards,

Paulo

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From:“Enders, Steve” <

To:

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Subject:Morenci cryptomelane dating

Date:Fri, 24 Sep 1999 09:10:47 -0700

MIME-Version: 1.0

X-WSS-ID: 1BF57DA740738-01-01

Dr. Renne,

> Joaquin Ruiz suggested I contact you about obtaining a 40Ar/39Ar

date on a sample of crytpomelane from the supergene profile at the

Morenci

copper deposit in southeastern Arizona. I have completed detailed XRD

study of the sample and confirmed its mineralogy. Although the sample is

very heterogeneous, it contains up to 70% cryptomelane, and variable

amounts of hollandite, todorokite, and a zinc-manganese-oxide along with

some quartz and trace amounts of sericite.

> I am in the final phases of work on my dissertation research into

the evolution of supergene enrichment at Morenci. A date on cryptomelane

from the supergene profile would be an excellent compliment to the

alunite

and jarosite dates for the deposit. I would like to wrap things up by

the

end of the year. Would you be interested in analyzing the sample, could

you provide me a relatively quick turn-around, and what would it cost?

> Thank you for your consideration of my request. Please advise at

your earliest convenience.

Cheers,

> Steve