Dont exactly know but you can see a paradigm of very old water entraped between Rocks in Kefalonia island Greece where it used to be the channel of Strabon , This water was founded and tested with Drills that a Professor of mine (Dr Mimides Theologos) did Many years ago and it is now mentioned in the Book Odysseus Unbound by Robert Bittlestone oxford university publications page 205 or others

http://books.google.gr/books?id=80Pg-LVkTVMC&pg=PA210&lpg=PA210&dq=the+real+ithaca+mimides&source=bl&ots=zDHZ-vPsXw&sig=FNpZUnND7FMH5CwAUncoVvV4ZLs&hl=en&sa=X&ei=qBXkUJumG-7Y0QWPtYGACA&ved=0CEAQ6AEwAw#v=onepage&q&f=false

http://books.google.gr/books?id=GcMHCR8P8ysC&pg=PA79&lpg=PA79&dq=the+real+ithaca+mimides&source=bl&ots=UGXrFLlEKY&sig=M1zVclMTwAhSYMC0C8lpERxzuxM&hl=en&sa=X&ei=qBXkUJumG-7Y0QWPtYGACA&ved=0CDsQ6AEwAg#v=onepage&q=the%20real%20ithaca%20mimides&f=false

It is suggested that Canadian Precambrian Shield brines could be connate water trapped since Devonian age.

Kindly provide a reference, please

Zhonghe, it seems that some of the oldest groundwaters are about 1 million year old and are found in Australia and Maryland (US), and the Sahara might have reserved that are about as old. They might be all young compare to the recent findings in South Africa. Check this link - there is also a reference to a Chemical Geology.

http://www.sciencedaily.com/releases/2011/02/110219202353.htm

The lead author of the paper is Johanna Lippmann-Pipke of the Helmholtz-Zentrum Dresden-Rossendorf in Leipzig, Germany. Researchers from that country, South Africa, the United States and Canada participated in the study.

Dr. Sherwood Lollar discussed the new findings at this year's meeting of the American Association for the Advancement of Science (AAAS) in Washington, DC on February 20, 2011.

I will check the CG paper when it comes out.

About the work of Lippmann, Sherwood Lollar and others the age of waters indicated is 1 billion years and not 1 million years. Chris Ballentine and Sherwood Lollar presented a work in my session at Goldschmidt 2012 on water in deep mines in Canada of 1.5 billion years old.

looks at : http://goldschmidt2012.conferencesymposium.com/june25/25-5.html

You can also give a look to 100 millions years old brines I recently published in 20111 in GCA on my research gate profile (you can download the text)