I have created a function to parse the "rawOutput" because the information provided by this function is quite useless.

function parseIdentify($info) {
    $lines = explode("\n", $info);
    
    $outputs = [];
    $output = [];
    $keys = [];
    
    $currSpaces = 0;
    $raw = false;
    
    foreach($lines as $line) {
        $trimLine = trim($line);
        
        if(empty($trimLine)) continue;
        
        if($raw) {
            preg_match('/^[0-9]+:\s/', $trimLine, $match);
            
            if(!empty($match)) {
                $regex = '/([\d]+):';
                $regex .= '\s(\([\d|\s]{1,3},[\d|\s]{1,3},[\d|\s]{1,3},[\d|\s]{1,3}\))';
                $regex .= '\s(#\w+)';
                $regex .= '\s(srgba\([\d|\s]{1,3},[\d|\s]{1,3},[\d|\s]{1,3},[\d|\s|.]+\)|\w+)/';

                preg_match($regex, $trimLine, $matches);
                array_shift($matches);
                
                $output['Image'][$raw][] = $matches;
                
                continue;
            }
            
            else {
                $raw = false;
                array_pop($keys);
            }
        }
        
        preg_match('/^\s+/', $line, $match);
        
        $spaces = isset($match[0]) ? strlen($match[0]) : $spaces = 0;
        $parts = preg_split('/:\s/', $trimLine, 2);
        
        $_key = ucwords($parts[0]);
        $_key = str_replace(' ', '', $_key);
        $_val = isset($parts[1]) ? $parts[1] : [];
        
        if($_key == 'Image') {
            if(!empty($output)) {
                $outputs[] = $output['Image'];
                $output = [];
            }
            
            $_val = [];
        }
        
        if($spaces < $currSpaces) {
            for($i = 0; $i < ($currSpaces - $spaces) / 2; $i++) {
                array_pop($keys);
            }
        }
        
        if(is_array($_val)) {
            $_key = rtrim($_key, ':');
            $keys[] = $_key;
            
            if($_key == 'Histogram' || $_key == 'Colormap') {
                $raw = $_key;
            }
        }
        
        $currSpaces = $spaces;
        $arr = &$output;
        
        foreach($keys as $key) {
            if(!isset($arr[$key])) {
                $arr[$key] = $_val;
            }
            
            $arr = &$arr[$key];
        }
        
        if(!is_array($_val)) {
            $arr[$_key] = $_val;
        }
        
    }
    
    $outputs[] = $output['Image'];
    
    return count($outputs) > 1 ? $outputs : $outputs[0];
}

Usage example:

$img = new Imagick('example.png');
$identify = parseIdentify($img->identifyImage(true)['rawOutput']);

But the "rawOutput" that this function returns only contains the first frame if it is a GIF. Alternatively you can use the command "identify" to get the data of all the frames:

$identify = parseIdentify(shell_exec('identify -verbose example.gif'));

If you use the option to append the raw output, you can extract the mime type from there.  I'm not sure what's going on in the background here, but it seems far less useful than the command line identify tool.

The array returned by Imagick::identifyImage():

Array
(
    [imageName] => /some/path/image.jpg
    [format] => JPEG (Joint Photographic Experts Group JFIF format)
    [geometry] => Array
        (
            [width] => 90
            [height] => 90
        )

    [type] => TrueColor
    [colorSpace] => RGB
    [resolution] => Array
        (
            [x] => 300
            [y] => 300
        )

    [units] => PixelsPerInch
    [fileSize] => 1.88672kb
    [compression] => JPEG
    [signature] => 9a6dc8f604f97d0d691c0286176ddf992e188f0bebba98494b2146ee2d7118da
)

Looks like the only way to get the mimetype is getimagesize()...