Hi gstyl,
As a quick solution , please refer to the steps below:
1. Login teamsite with administrator account.
2. Create the document library which visible only by administrator
To do this click Libraries then click Create, select Document Library enter the Library name and click Create.
3. Add the users which you would like to let them have administrator permission into Viewers Group.
To do this click Site Actions, select Site Settings, click Site permissions, select Team Site Owners Group and add users.
4. Click the library which you created in the Libraries , Upload a file.(It’s important, if the library is empty , you cannot setup library permission.)
5. In the ribbon banner, Click Library which under Library Tools, then click Library Permissions which under Settings.
6. In this Permissions Tools, click Stop Inheriting Permissions then click OK, so This list item has unique permissions.
7. Select all the permissions in this list and click Remove User Permissions, after remove these permissions you can grant permissions that who can view and who can edit this list item.
8. Click Grant Permissions and add Team Site Owners Group with Full Control permissions, click OK.
9. After you finish these operates, only Team Site Owners user can view and edit it.
Thanks,
Alex Du