This method of deploying a newer version of a prior established website to a different domain is very much flawed as you've probably come to realize now from comments and posts above, mainly relating to the issues of page rank effect of aged domain and index history, the duplicate content issue and the 301 redirects.

I would strongly recommend your next steps to be:

1. Change your .eu domain to use a 301 redirect pointing to the old domain.
2. Either commit to publishing the new site on the old domain (taking the old site offline), or keeping the old site published for the moment, and taking the new site offline.
3. Ensure that if any of the URL's have changed for the site in the process of your new opencart implementation and SEO work, make sure you setup appropriate 301 redirects in an htaccess at the root of your site for all currently indexed pages to point them to the right corresponding pages on the new site (this can be quite a big job if its a large product catalogue!).

Hope this helps.

This method of deploying a newer version of a prior established website to a different domain is very much flawed as you've probably come to realize now from comments and posts above, mainly relating to the issues of Page Rank effect of aged domain and index history, the duplicate content issue and the 301 redirects.

I would strongly recommend your next steps to be:

1. Change your .eu domain to use a 301 redirect pointing to the old domain.
2. Either commit to publishing the new site on the old domain (taking the old site offline), or keeping the old site published for the moment, and taking the new site offline.
3. Ensure that if any of the URL's have changed for the site in the process of your new opencart implementation and SEO work, make sure you setup appropriate 301 redirects in an htaccess at the root of your site for all currently indexed pages to point them to the right corresponding pages on the new site (this can be quite a big job if its a large product catalogue!).